There is nothing ---but---down and wait for him to come back
问题描述：
There is nothing ---but---down and wait for him to come back
A to be done ,to sit B to do ,sit
C done,to sit D to do,sit
答
B D都可以（因为他们一模一样）.noting to do .A前面这个表达因该可以,但是to sit就有点问题.可以看到sit后面有个并列连接词and,而and 后的wait是原形的（可以看出sit和wait是两个平行的词汇）.所以保持句子平衡,选sit