酸雨的危害表现在[ ]
A．腐蚀建筑物和户外雕塑
B．使农作物枯萎，甚至死亡
C．使土壤、河流、湖泊酸化
D．以上三项都是
答案：D
聚酰胺薄层色谱法特别适合于分离哪类化合物（）
A.酚类
B.黄酮类
C.皂苷类
D.醌类
E.萜类
---How was their last weekend?
---Great. They had a picnic in the park and enjoyed _______.
A．them
B．they
C．their
D．themselves
