语法

语法点：现在完成进行时 (Present Perfect Continuous)

现在完成进行时 have / has been + doing 用来表示一个动作从过去某一点开始，一直持续到现在，而且往往还在继续或刚刚结束。它强调的是“过程还在延续”，而不是结果。常和 since（自从……）、for（持续多久）、all day、recently 等时间状语连用。本课消防员扑灭大火之后，“从那时起一直在查找起火原因”，用的就是 have been trying：调查从过去开始，到说话时仍在进行。对比现在完成时 have put out（火已经扑灭，强调结果）就能看出两者的区别。

结构

形式	结构	例句
肯定	主语 + have / has been + 动词-ing	They have been trying to find out how the fire began.
否定	主语 + have / has not been + 动词-ing	They have not been looking for broken glass.
一般疑问	Have / Has + 主语 + been + 动词-ing?	Have they been trying to find the cause?
特殊疑问	疑问词 + have / has + 主语 + been + 动词-ing?	How long have they been trying?

常用时间状语：since then / since Monday, for two days, all morning, recently, lately。

课文中的例句

[句 2] Since then, they have been trying to find out how the fire began. — since then 引出起点，have been trying 表示调查从那时持续到现在
[句 1] At last firemen have put out a big forest fire in California. — 现在完成时 have put out 强调“已经扑灭”这个结果，与句 2 的“仍在进行”形成对比
[句 4] Yesterday the firemen examined the ground carefully, but were not able to find any broken glass. — 有明确的过去时间 yesterday，只能用一般过去时，不能用完成时态
[句 6] This morning, however, a fireman accidentally discovered the cause. — 调查过程中发生的一次性动作，用一般过去时

补充例句

The firemen have been examining the ground since this morning. — 消防员从今天早上起一直在检查地面。
It has been raining for three days, so there will be no forest fires. — 雨已经下了三天，所以不会有森林火灾。
I have been trying to solve this mystery all week. — 我整个星期都在设法解开这个谜。

易错点

❌ Since then, they are trying to find out how the fire began. → ✅ Since then, they have been trying to find out how the fire began. — 有 since 表示“从过去持续到现在”，要用现在完成进行时，不能用一般现在进行时。
❌ They have been trying to find the cause since two days. → ✅ They have been trying to find the cause for two days. — since 后面接起点，for 后面接一段时间。
❌ Yesterday the firemen have been examining the ground. → ✅ Yesterday the firemen examined the ground. — yesterday 是明确的过去时间，只能用一般过去时。
❌ He has been knowing the answer since this morning. → ✅ He has known the answer since this morning. — know、have（拥有）等状态动词一般不用进行时。

逐句语法分析 · 12 句

1At last firemen have put out a big forest fire in California.
消防队员们终于扑灭了加利福尼亚的一场森林大火。
现在完成时 (Present Perfect) · At last + 主语 + have + 过去分词 + 宾语 + 地点状语
- have put out 强调火“已经扑灭”这一结果
- put 的过去分词仍是 put
- at last 表示“终于”
现在完成时说明扑火这一动作已经完成并对现在有影响，与后文的“仍在调查”形成对比。
2Since then, they have been trying to find out how the fire began.
从那时起，他们一直在设法查明火灾是怎么发生的。
现在完成进行时 (Present Perfect Continuous) · Since then, + 主语 + have been + 动词-ing + 不定式 + how 从句
- have been trying 表示动作从过去持续到现在
- since then 是完成时态的标志
- how the fire began 是宾语从句，用陈述语序
本课的核心句。调查从大火扑灭后开始，一直持续到现在，所以用现在完成进行时。
3Forest fires are often caused by broken glass or by cigarette ends which people carelessly throw away.
森林火灾常常是由人们随手扔掉的碎玻璃或烟头引起的。
一般现在时被动语态 (Simple Present Passive) · 主语 + are + often + 过去分词 + by + 施动者 + which 定语从句
- are caused by 表示普遍事实的被动语态
- which people carelessly throw away 修饰 cigarette ends
陈述森林火灾的常见原因，用一般现在时被动语态；定语从句说明烟头是被随意丢弃的。
4Yesterday the firemen examined the ground carefully, but were not able to find any broken glass.
昨天消防队员们仔细检查了地面，但没有发现任何碎玻璃。
一般过去时 (Simple Past) · Yesterday + 主语 + 动词过去式 + 宾语, but + were not able to + 动词原形
- yesterday 决定全句用一般过去时
- were not able to = could not
- any 用于否定句
有明确的过去时间 yesterday，只能用一般过去时，不能用完成时态。
5They were also quite sure that a cigarette end did not start the fire.
他们还非常肯定，火灾不是烟头引起的。
一般过去时 (Simple Past) · 主语 + were + quite sure + that 从句（did not + 动词原形）
- be sure that 后接宾语从句
- did not start 是一般过去时的否定形式
主句和从句都用一般过去时，叙述昨天的判断；否定用 did not + 动词原形。
6This morning, however, a fireman accidentally discovered the cause.
然而今天上午，一位消防队员偶然发现了起火的原因。
一般过去时 (Simple Past) · This morning, however, + 主语 + 副词 + 动词过去式 + 宾语
- this morning 作过去时间状语
- however 放在句中，前后用逗号隔开
- accidentally 修饰 discovered
叙述今天早上发生的一次性动作，用一般过去时；however 表示转折。
7He noticed the remains of a snake which was wound round the electric wires of a 16,000-volt power line.
他注意到一条蛇的残骸缠绕在一条16000伏高压电线上。
一般过去时 (Simple Past) · 主语 + noticed + 宾语 + which + was wound round + 名词短语
- was wound 是 wind（缠绕）的过去时被动
- which 引导定语从句修饰 a snake
- 16,000-volt 作前置定语
主句一般过去时；定语从句用被动语态说明蛇“被缠在”电线上。
8In this way, he was able to solve the mystery.
就这样，他解开了这个谜。
一般过去时 (Simple Past) · In this way, + 主语 + was able to + 动词原形 + 宾语
- was able to 表示过去某次成功做成某事
- in this way 意为“就这样”
was able to 强调一次性成功，比 could 更合适。
9The explanation was simple but very unusual.
解释很简单，但却非常不同寻常。
一般过去时 (Simple Past) · 主语 + was + 形容词 + but + 副词 + 形容词
- 系动词 was + 表语
- simple but very unusual 两个形容词并列
主系表结构，but 连接两个对比的形容词。
10A bird had snatched up the snake from the ground and then dropped it on to the wires.
一只鸟从地上抓起了这条蛇，然后把它扔到了电线上。
过去完成时 (Past Perfect) · 主语 + had + 过去分词 + 宾语 + and then + 过去分词 + 宾语
- had snatched up 表示发生在起火之前的动作
- and then dropped 共用助动词 had
- on to the wires 表示方向
解释起火原因时回到更早的过去，所以用过去完成时；两个动作用 and then 连接。
11The snake then wound itself round the wires.
接着，蛇就把自己缠在了电线上。
一般过去时 (Simple Past) · 主语 + then + 动词过去式 + 反身代词 + round + 宾语
- wound 是 wind 的过去式
- itself 是反身代词，表示蛇把自己缠上去
承接上一句的顺序，用一般过去时；wound itself round 表示主动缠绕。
12When it did so, it sent sparks down to the ground and these immediately started a fire.
蛇这样一缠，就把火花送到了地面上，火花立刻引起了大火。
一般过去时 (Simple Past) · When 从句 + 主语 + 动词过去式 + 宾语 + and + 主语 + 副词 + 动词过去式 + 宾语
- did so 代替前面提到的动作
- sent sparks down 表示火花落向地面
- these 指代 sparks
when 从句和主句都用一般过去时，叙述连续发生的动作。

练习 · 44 题

每组做完自动记录；总正确率 80% 以上记为掌握 ★。改写和改错与参考答案不完全一致时，登录用户由 AI 判断是否可接受。

总计 0/44

选择正确的答案
1. Since then, they ____ to find out how the fire began.
选择正确的答案
2. The firemen have been examining the ground ____ this morning.
选择正确的答案
3. They have been looking for the cause ____ two days.
选择正确的答案
4. ____ the firemen been trying to find out how the fire began?
选择正确的答案
5. At last firemen ____ a big forest fire in California.
选择正确的答案
6. Yesterday the firemen ____ the ground carefully.
选择正确的答案
7. How long ____ trying to solve the mystery?
选择正确的答案
8. Forest fires are often ____ by broken glass or cigarette ends.
选择正确的答案
9. A bird ____ the snake from the ground and then dropped it on to the wires.
选择正确的答案
10. In this way, he was able to ____ the mystery.