题干
I saw some trees the leaves of _____ were black with disease.
A：that
B：which
C：it
D：what
答案(点此获取答案解析）
B
A：that
B：which
C：it
D：what
；②沼气和天然气
都是可再生能源；③冰和干冰既是纯净物又是化合物；④不锈钢和目前流通的硬币都是合金；