1 to turn one's back on someone
Back是指人体的后背。从字面上解释，就是把自己的背对着某人。可是，实际上这是指根本不理会某人，或不肯给那个有困难的人任何帮助，即不理会某人、不愿帮助某人。
例如：I won't ever forgive my older brother--he turned his back on me and refused to lend me any money when I lost my job.
我永远也不会原谅我的大哥哥。当我失去我的工作的时候，他根本不肯帮忙，一点钱都不愿意借给我。
又如：My father deserted my mother and me when I was five years old. But I can't turn my back on him now that he's old and sick. So I'm paying the rent for him on a little apartment in Los Angeles.
当我五岁的时候，我爸爸抛弃了我妈妈和我。可是，现在我爸爸又老又病，我可不能不管。他现在在洛杉矶租了一个小公寓套房，我替他付房租。
2 to scratch one's back
要是你觉得背上某一个地方痒痒，而你自己又抓不到，这是很难受的。这时候，最好有人替你抓一下。To scratch one's back从字面上来看就是“抓某人的背”。它的真正含义是：某人帮了你一下忙，而这个帮你忙的人也期望你下回帮他的忙。因此，to scratch one's back实际上就是：这回你帮我忙，下回我就帮你的忙。
例如：This senator from the 11th district scratched my back when he voted for my bill to cut state income taxes, so it's my turn to do him a favor and vote for that bill for more money for roads in his district.
上回在投票通过我提出的有关裁减州所得税的提案时，第十一选区的参议员投了我一票，帮了我的忙。所以，现在是该我帮他忙的时候了，我得投票赞成为他的选区修建公路增加拨款的提案。
又如：In my business it's important to scratch each other's back. Say a customer does me a favor by giving me an extra big order. The next time he's in town I might take him out to dinner and a Broadway show.
干我们这行，相互帮忙是很重要的。要是一位顾客订了特别大的一批货，帮了我的忙，下次他再到这个城市来的时候，我可能得请他吃晚饭和到百老汇去看演出。
