unless 用法--shall we go on a picnic this weekend?---good idea,unless it____选rains 还是 doesn't rain?

你好,我认为应该选rains .意思为“好主意,除非下雨（就不去了）”.
Unless: conj. 除非, 如果不
unless是从属连词,引导条件状语从句,含有否定意义,相当于if条件状语从句的否定形式.所以unless = if not.注意：unless引导的条件状语从句和if条件状语从句,与其它时间状语从句一样,用一般现在时代替将来时.
1. Unless you take more care, you’ll have an accident.
(如果不多加小心的话,你会出事故的.)
2. My baby sister never cries unless she is hungry.
(我那刚出生的妹妹除非饿了,否则她是从来不哭的.)
3. Unless bad weather stops me, I jog every day.
(除非坏天气阻拦我,否则每天我都慢跑的.)