at most最多;最大

　　We can stay for two days at most.

　　我們最多能待兩天。

　　at no time 從不;決不

　　At no time will China be the first to use nuclear weapons.

　　at once馬上，立刻;同時(shí)

　　Do it at once. 馬上做。

　　Dont all speak at once! 大家別一塊兒說(shuō)話(huà)!

　　at one time曾經(jīng)，一度;同時(shí)

　　at present現(xiàn)在;目前

　　At present, he is on holiday.目前，他正在度假。

　　at the cost of犧牲，以…為代價(jià)

　　at the moment此刻，目前

　　at the same time同時(shí)，然而，不過(guò)

　　at times有時(shí)

　　B

　　back and forth前后;來(lái)回

　　Someone was pacing back and forth behind the curtain. 有人在幕布后踱來(lái)踱去。

　　back down 放棄要求，讓步

　　They refused to back down.他們不愿讓步。

　　Since most of the people present agreed with her, I had to back down. 大多數(shù)到

　　會(huì)的人都同意她的意見(jiàn),我只好放棄原來(lái)的意見(jiàn)了。

　　He has backed down from the position he took last week.

　　他已放棄他上星期所采取的立場(chǎng)。

　　The speakers forceful words persuaded his opponent to back down.

　　back up支持;堵塞;后退

　　Most members were against Mr. Jones, who would have lost his position if you had

　　n’t backed him up.

　　The new evidence backed up my argument.

　　新的證詞有助于我的論點(diǎn)。

　　‘Dont shoot!’ he said and backed up.

　　“別開(kāi)槍!” 他說(shuō)著往后退。

　　Will you back me up in the argument.

　　be about to剛要，即將

　　bear / keep in mind牢記在心

　　You must bear in mind that your parents hope to depend on you to become a good doctor.

　　你要記住你的父母指望你成為一名好醫(yī)生。

　　before long不久以后

　　Before long, the noise dropped completely and the boat began to drift gently across the water. 不久,轟鳴聲完全消失了,于是這只船開(kāi)始慢悠悠地漂浮在水面上。

　　beside point離題;不相干的