擅长高中英语单选的进！急！！！！

(1)I'll tell him about the meeting __B____he comes back. 他一回来我就告诉他关于这个会议。
A.once B. as soon as C.unless D.while
once 连接词 conj. 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

as soon as作“一…就”解，引导时间状语从句

unless 连接词 conj. 1.如果不,除非
I won't apologize unless she apologizes first.
除非她先道歉,否则我不道歉。
介词 prep. 1.除...外

while 连接词 conj.
1.当...的时候,和...同时
She listened closely while he read the letter.
他读信时,她听得很仔细。
I'll take care of your children while you are away.
你不在时我会照顾你的孩子的。
We must strike while the iron is hot.
我们必须趁热打铁。
2.而,然而
I like tea while she likes coffee.
我喜欢喝茶,而她喜欢喝咖啡。
3.虽然,尽管
While I like the color of the hat, I do not like its shape.
虽然我喜欢这顶帽子的颜色,但我不喜欢它的形状。
4.只要

(2)If you want to pass your exams, you'd better change your___C__
A.excuse B.message C.at