用所给词的适当形式填空。

1. Our headmaster invited a singer ________ (sing) for us this morning.

2. I _______ (clean) my room at 9:00 last Sunday.

3. They can do that thing by ________ (they).

4. I think _______ (predict) the future is a bit difficult.

5. The teacher told us that light ________ (travel) much faster than sound.

读我国局部地区图，完成小题。

小题1:图中A、B、C、D四处，土壤最肥沃的是                    (　　)。

A．A处                         B．B处

C．C处                         D．D处

小题2:影响华北地区农业发展的主要限制性因素是                 (　　)。

A．灌溉水源短缺

B．水土流失加剧

C．作物种植结构单一

D．农业经营方式粗放小题3:该地区发展农业应采取的主要措施是                       (　　)。

A．退耕还林还草，改善生态环境

B．增施化肥和农药，提高粮食单产

C．扩大耕地面积，提高粮食商品率

D．加强水利建设，确保高产稳产