问题补充：
John studied very hard last year. .
A. So was his deskmate.
B. So his deskmate was.
C. So did his deskmate.
D. So his deskmate did.
答案：
A. So was his deskmate.
B. So his deskmate was.
(答案→)C. So did his deskmate.
D. So his deskmate did.
解析：“so＋助动词（情态动词或连系动词）＋另一主语”，此句型是主谓倒装结构，可以表示前面的情况也适用于后者，使用该句型需要注意以几个方面的问题： 1．该句型只能用于肯定句，不能用于否定句：如果前句是否定句，则要用“neither /nor ＋助动词＋主语”。 2．句型中的主语与上文中的主语是不同的两个主语3．句型中助动词，包括连系动词和情态动词的时态要和上句中谓语动词的时态相一致。结合语境可知前文情况也适用于后者,故用主谓倒装结构,选C.
