In time of serious accidents, _______ we know some basic things about first aid,we can save lives.
A. whether B. until
C. if D. unless
In time of serious accidents, _______ we know some basic things about first aid,we can save lives.
A. whether B. until
C. if D. unless
C
句意为“在遇到严重事故时，如果我们知道一些急救方面的基本知识，我们就能救人命”。If引导条件状语从句表示“如果” 时，不可用whether替换。