金锁固精丸的组成中有（）
A.沙苑蒺藜
B.白蒺藜
C.罂粟壳
D.山茱萸
E.肉豆蔻
参考答案：A
The old man __________ in Tibet for two years as a volunteer teacher；it is an experience he often mentions.
A．served
B．serves
C．is serving
D．has served
地下水可分为哪几类？简述其特点。
