目前土地资源丧失和破坏的主要原因是[ ]
A．水土流失
B．气候变暖
C．种植树木
D．过度放牧
A
How time flies! It's in two months ________ we'll say goodbye to our high school life.
A．before
B．that
C．until
D．when
试举例说明抗菌药物抑制和杀灭细菌的作用机制。
