if..,be sure
问题描述：
if..,be sure
If you have any trouble,be sure to call me.
if sunday is convenient for you,be sure to come to get toghter
这里怎么没有一个主句啊.be sure这个是句子吗?为什么没有主语?
答
be sure这个是句子,是祈使句句,主语省略不写了.补充完整应是If you have any trouble,you are sure to call me.
if sunday is convenient for you,you are sure to come to get toghterThousands of foreigners were attracted to the Shanghai World Expo the day it opened.the day 后面的when为什么没了？