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《名词性从句之表语从句的使用》 高三三轮冲刺复习
（考点精讲·易错突破·真题实战）
一、表语从句的定义与位置
表语从句（Predicative Clause）属于名词性从句的一种，在句中充当表语，位于系动词（如be, seem, appear, remain等）之后，对主语进行补充说明。其基本结构为：
主语 + 系动词 + 连接词 + 表语从句
例句：
The problem is that we lack enough time.
What surprised me was how he solved the problem quickly.
二、表语从句的三大连接词
1. 连接词 that
功能：仅起连接作用，无实际意义，且不可省略。
例句：
The truth is that he didn’t tell a lie.
My suggestion is that we should start early.
2. 连接词 whether
功能：表示“是否”，不可用 if 替换（表语从句中只用 whether）。
例句：
The question is whether they can finish the task on time.
His doubt is whether the plan will work.
3. 疑问词（what, when, where, why, how, who, whom, whose）
功能：在从句中充当成分（主语、宾语、状语等），有实际含义。
例句：
That is why I refused the offer. （why 作原因状语）
The key point is what we should do next. （what 作宾语）
三、表语从句的特殊用法与注意事项
1. 虚拟语气在表语从句中的使用
当主语为表示“建议、要求、命令”的名词（如 suggestion, advice, order）时，表语从句需用 “(should) + 动词原形” 的虚拟语气结构。
例句：
My advice is that you (should) apologize to her.
The order was that all soldiers (should) stay alert.
2. 表语从句中的 “as if/as though”
表示“好像”时，可用 as if/as though 引导表语从句，从句中根据语境选择陈述语气或虚拟语气。
例句：
It looks as if it is going to rain. （陈述语气，可能真实）
He talked as though he had known everything. （虚拟语气，与事实相反）
3. 表语从句与 “because” 的灵活使用
在强调句型或口语中，可用 because 引导表语从句，但需注意逻辑合理性。
例句：
The reason he was late is because his car broke down. （口语化表达）
对比正式表达：The reason he was late is that his car broke down.
四、表语从句的易错点与解题技巧
易错点1：混淆 that 与 what
错误：The difficulty is that we need to solve.
修正：The difficulty is what we need to solve. （what 在从句中作宾语，that 无实际意义且不充当成分）
易错点2：误用 if 替代 whether
错误：The question is if he will come.
修正：The question is whether he will come.
易错点3：忽略虚拟语气
错误：His suggestion is that we will reduce costs.
修正：His suggestion is that we (should) reduce costs.
五、高考真题实战演练
例题1（2023年新高考I卷）：
The reason why he failed the exam was ______ he spent too much time playing games.
A. because B. that C. why D. what
答案：B
解析：表语从句中正式表达用 “that”，避免重复 “reason...because” 的逻辑错误。
例题2（2022年全国甲卷）：
What the teacher emphasized was ______ we should review the key points.
A. if B. whether C. that D. what
答案：C
解析：表语从句中需用 that 引导，强调内容。
六、巩固练习与总结
练习1：用表语从句合并句子
The problem is this. How can we protect the environment
→ The problem is how we can protect the environment.
练习2：改错
His idea is if we can find a cheaper solution.
→whether
总结口诀：
表语从句跟系动，连接词要记心中；
that 无义 whether 疑，疑问词在句中用；
虚拟语气别遗漏，易错点要练贯通！

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