on the average (=on average， on an average)平均

(be) aware of (=be conscious of ， having knowledge or consciousness)意识到，知道。

at the back of (=behind)在…后面

in the back of在…后部(里面); on the back of在…后部(外面); be on one’s back(=be ill in bed)卧病不起。

at one’s back(=supporting or favoring sb.)支持，维护; have sb. at one’s back有…支持，有…作后台

turn one’s back on sb. (=turn away from sb. in an impolite way)不理睬(某人)，背弃，抛弃

behind one’s back背着某人(说坏话)

be based on / upon基于

on the basis of根据…，在…基础上

beat…at在…运动项目上打赢