1.While 通常是用来把长动作和长动作串联起来的连词。eg: I was watching TV while my brother was playing computer at this time yesterday.2.the moment 通常在前面加at 来作为时间状语用，意为：此刻;当时。eg: I am very busy at the moment. 我此刻/现在很忙。 moment 还有其他的用法。例如：a moment ago （用过去时） at that moment （用过去时或过去进行时） 等等。 3.once 有不同的解释。(列举了ABC三种)A.副词 ad.
a.一次,一回
I see them once every two months.
我每两个月与他们见一次面。 b. 昔日,曾经
He once knew her, but they are no longer friends.
他以前认识她,但他们已经不是朋友了。 B.名词 n. a. 一次,一回
Once is enough.
一次就够了。
C.连接词 conj.
a. 一旦,一经...便
Once you get into a bad habit, you'll find it hard to get out of it.
一旦染上坏习惯,想改掉就难了。
