Question

—We’ll visit the Summer Palace_____ there is a heavy rain tomorrow.
— OK! Boating on the lake must be great fun.

A．if

B．as soon as

C．unless

D．since

Answer 1

C

考察连词。if 如果；as soon as一……就；unless 除非；since自从……以来。句意：我们要去参观颐和园，除非明天有大雨。——好吧，在湖上泛舟肯定很有趣。故选C。
故选C