单选题 All ______ is a steady supply of water to the farmland.
A. which needs B. that is needed C. the thing is needed D. need

【正确答案】 B
【答案解析】[解析] 句子的大意为：所需要的就是对农田用水的稳定供应。本句主语为不定代词all，“that is needed”为主语的定语从句。所以B项符合题意。