I saw a boy fall off a bike,这句话saw用了过去式,为什么fall不用?

I saw a boy fall off a bike,这句话saw用了过去式,为什么fall不用? I saw a boy fall off the bike and hurt himself.还是I saw a boy falling off the bike and hurting hiI saw a boy fall off the bike and hurt himself.还是I saw a boy falling off the bike and hurting himsilf。 i saw a boy ()into the river.用fall还是falling? l saw a little boy fall into the water.是用fall还是falling? 问个高二英语改错题．．．We saw a boy fall off his bike ahd he began to cry.老师说这句话对的,但我觉得off后面应该有个from啊.谁能帮我解答下? The boy was seen___(fall) off his bike a moment ago. I am a boy but fall in love with boy,what should I do? I saw a boy ____(run)from the cinema then. 【高二英语】单选：While watching the boy fall off the tall tree,I stood there,_____ out of my mind.While watching the boy fall off the tall tree,I stood there,_____ out of my mind.A.terrifyingB.being terrified C.terrifiedD.having terrified i saw a saw saw a saw. i saw with my own eyes the boy fall from the tree这里的fall是什么用法,为什么不是falling或 fallen 英语（过去进行时）1、What book ___you ___ when I ___ you at four yesterday afternoon?A.did,read,was seeing B.did,read,saw C.were,reading,saw D.were,reading,was seeing2、A girl ___ my pen fall off the tavle when she ___ me .A.saw,passed B.w i saw a boy.the boy was playing with a cat.i saw a boy _ _ _ _ a cat合并为一句 l saw a little boy fall into the water.为什么不用fell,而用fall?为什么不用它的过去式呢,不是已经发生 i saw a saw saw a I never saw a saw saw a I saw a saw swa a saw. They are afraid I'll be knocked down by a truck ,fall off a tree,or fight with others.其中fall off a