A greenhouse is a building of glass for keeping plants warm when the outside temperature is low..
A. made, which is used
B. which is made, is used
C. made, being used
D. is made, used
网友回答
(答案→)A. made, which is used
B. which is made, is used
C. made, being used
D. is made, used
解析：第一空考查非谓语动词，用过去分词作定语修饰a building，第二空是定语从句，which 在从句中做主语，短语：be used for 被用来做某事，所以选A。