比较状语从句：
than, as…as…，not so as…，(not) the same as, the+比较级;
eg：Light travels fast than sound.
the+比较级：
eg：The sooner，the better.
eg：Girls are thus seen as less valuable than boys and art kept at home to do housework while their brothers are sent to school - the prophecy(预言) becomes self- fulfilling, trapping women in a vicious circle (恶性循环) of neglect.
(1)当……的时候：while, when, as ;
when：强调一件事情正在发生的时候，另外一件事情突然发生;
eg：When I was watching TV, my mother came back.
while：强调两个动作同时进行，一边……一边……;
eg：My father is cooking while my mother is reading newspaper.
as："随时间推移"
eg：As time went by, the days became longer and longer.
