一.选B,slipped on。
二.fell down和slipped on都要摔倒的意思。
三.fall down是不及物短语,后面不能接名词,除非有fall down后面还有一个介词,但是这里没有。举例:
1.Babies often fall down when they are learning to walk. 小儿学步时常会跌跤。
2.It doesn't matter how many times you fall down.
摔倒多少次不要紧,要紧的是你能多少次爬起来。
四.slip on是一个及物短语,后面可以接名词,在这里是the carpet。
1.She slipped on the ice and broke her leg. 她在冰上滑倒把腿摔断了。
2.I was unlucky to slip on a banana skin and fall over. 我真倒霉,踩在香蕉皮上滑倒了。