Question

英语题求解析

A policeman often has to control traffic, either（ ）foot in the center of a town,
or in a police car on the roads. I
A. on B.by c.under D. with
为什么不可以用by

Answer 1

没有这个用法，有by bike,by bus,by car on foot.on foot站着。警察站着指挥交通，没毛病。补充一点儿:stand on your knees.跪着。(双膝跪地)

Answer 2

on foot是一个词，步行