keep back留存，保留（…的一部分）；隐瞒；保密；
keepv.(使)保持，处于;继续，重复(做某事)；使耽搁；使延误
Police had to erect barriers to keep crowds back.
警察得设立路障来阻截人群。
Why do they keep passing back to the goalie?
他们为什么总是把球回传给守门员？
Neither of them is telling the whole truth. Invariably, they keep something back.
他俩谁也没把全部实情都说出来。他们总是要隐瞒些什么。
