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
begin with 以…开始;to begin with(=first of all)首先，第一(经常用于开始语)
on behalf of(=as the representative of)以…名义
believe in(=have faith or trust in;consider sth. sb. to be true)相信，依赖，信仰
benefit(from)受益，得到好处.
for the benefit of 为了…的利益(好处)
