问题补充：
Clean water and fresh air are essential for our daily life, we can’t live.
A. by which
B. without which
C. that
D. on which
答案：
A. by which
(答案→)B. without which
C. that
D. on which
解析：句意：干净的水和新鲜的空气是我们日常生活中必不可缺少的，没有它们我们就不能活。此处Clean water and fresh air是先行词，在定语从句中在介词的宾语。故选B。
