when someone ___ahead of you opens the door for you.A walks B walking C is walking 选哪个为什么谢
问题描述：
when someone ___ahead of you opens the door for you.A walks B walking C is walking 选哪个为什么谢
答
B
分词形式做定有修饰someone,表示主动状态“走在你前面的某个人”