选哪个为什么?1.what happened yesterday?.we were planting tress___it began to rainA.while B.when C.as soon as D.until

选哪个为什么?1.what happened yesterday?.we were planting tress___it began to rainA.while B.when C.as soon as D.until
选哪个为什么?
1.what happened yesterday?
.we were planting tress___it began to rain
A.while B.when C.as soon as D.until

选哪个为什么?1.what happened yesterday?.we were planting tress___it began to rainA.while B.when C.as soon as D.until
B
前一句（我们正在植树）用的是过去进行时,表示过去某一时间内（正在）进行的动作,也可表示一个动作正在进行时,另一个动作发生了或一动作正在进行时,另一动作同时正在进行.
后一句（开始下雨了）用的是一般过去时,表示过去某个时间里发生的动作或状态.
由于前一句表达的是植树这个动作正在进行,所以下雨这个动作是发生在我们植树过程中的,这两个动作是同时发生的.
A、B都能表示两个动作同时进行,A后跟的是延续性动词,而开始下雨是非延续性的,只是一瞬间的,不可能一直都在开始下雨,B后可跟延续性动词也可跟非延续性动词,所以选择B

D

D我们种植树，直到它开始下雨

D