题目内容：

( )you have worked out the first problem,you may go on to work on the second
( )you have worked out the first problem,you may go on to work on the second
A.even if B.unless C.now that Dthough

优质解答

C 既然,表原因
A 即使,表让步
B 除非,表条件
D 虽然,表让步
既然你已经做出第一道题了,现在可以做第二道了

追问：

B.unless 为何不对？

追答：

如果选B除非，应该说才除非你做对第一个题，否则就不能做第二题 那后半句应该用否定 Unless you have worked out the first problem, you may not go on to work on the second

追问：

那和时态 have worked out the first problem有没有影响？