- 疑问：什么时候用复数？
1. that引导的主语从句
a.that在句中不做成分。当主语从句位于句首时，不能省略：
Thathe likes books of this kind is very interesting.= It’s very interesting (that)he likes books of this kind.
b. 当谓语动词是seem,appear,bea pity.be a wonder,be likely等时，使用形式主语It，而将真正的主语放在句尾，这时从属连词that可省略：Itappeared to scientists on earth (that) the stars had moved.
2. Whether/if引导的主语从句
a. 表不确定的主语从句位于句首的时候则必须用whether，不能用if.
b. 如果用It 作形式主语时,whether和If都可以引导主语从句。
3. what引导的主语从句（其实是连接代词/连接副词啦）
a.what 引导主语从句，在从句中充当主语、宾语。
Whathe often holds in his hand is a dictionary. = He often holds a dictionary inhis hand.
b. who,whatever, whoever, whose, who 可引导主语从句，在从句中充当成分。
c.Where/when/how/why也可引导主语从句， 在从句中充当状语。
d. 注意that和what引导主语从句时候的区别：that不做成分，what做成分：
Whatyou said about him makes him sad. what在主语从句中做said的宾语
Thatyou don’tlike him makes him sad. that在主语从句中不做成分
4. 注意使用主语从句时，主句的谓语动词单复数。基本原则是，一般用单数（因为是一个从句么，从句一般都是单数）；但是如果根据主句上下文确定是复数，那么谓语动词也应该用复数。
a.(OG)What scientists know about dinosaur brains comes from studies of thecranium, the bony house of the brain located in the back of the skull.
这里whatscientists know about dinosaru brains这个主语从句后面的谓语动词应该用单数（comes）。
b. 另外一个OG/PREP例子：
Whatis much more difficult to determine is the reason for their decoration,the useto which primitive people put the caves, and the meaning of the magnificentlydepicted animals.
这里也用is，因为what的主语从句时单数
c.
网上的资料：What Ineed is money./What I need are books. 这里what I need这个主语从句后面的谓语动词应该根据后面的名词来决定（IT is money/THEY are books），所以一个用is, 一个用are
Performed last weekend were three plays. (correct) （这里没有主语，介词前面是个状语。所以由three plays来决定）
*Performed last weekend was three plays. (incorrect)
Sophocles's Oedipus cycle is three plays. (correct) （这里cycle是主语，所以还是单数）
*Sophocles's Oedipus cycle are three plays. (incorrect)
5. 如果由and连接两个或两个以上的主语从句作主语时，谓语动词用复数；由两个或多个连接词引导一个主语从句，谓语动词用单数。
When they will start and where they gohave not been decided yet.
When and wherethe meeting will begin has not been decided .
