用所给动词的适当形式填空

小题1:We will visit the farm if it ____________ (not rain) tomorrow。

小题2:Gravity is a force that stops us from____________ (float) in the air.

小题3:Our home town ___________(change) a lot over the years.

小题4:The train _______________( leave) already when we arrived.

小题5:I _________________( do) my homework when the light went out yesterday.

商品经济产生的一般条件是（）

A.产业革命

B.科技革命

C.社会分工

D.国际贸易