问题补充:
— What’s your plan for this weekend?
— We will go for a picnic by the river it rains.
A. unless
B. if
C. but
D. because
答案:
(答案→)A. unless
B. if
C. but
D. because
解析:unless除非,如果不;if是否,如果;but但是,可是;because因为;句意:你这个周末的计划是什么?——如果不下雨,我们要去河边野餐。计划语境可知选A。