问题补充：
–How come ?—I had to look after my sick brother.
A. didn’t you come to the party yesterday
B. did you not come to the party yesterday
C. you didn’t come to the party yesterday
D. you came to the party yesterday
答案：
A. didn’t you come to the party yesterday
B. did you not come to the party yesterday
(答案→)C. you didn’t come to the party yesterday
D. you came to the party yesterday
解析：句意：昨天你怎么没来参加聚会？我必须照顾我生病的弟弟。How come 的用法大部分就等于 why，虽然 how come 跟 why 的用法上差不多, 但二者的问法不同. 例如, Why didn’t you come to the party yesterday 换成 how come 的话, 要说成, How come you didn’t come to the party yesterday 。 注意一下, 这二者的助动词动词位置是不一样的.故选C.
