If you swim in a river or lake, be sure to investigate is below the water surface. Often there are rocks or branched hidden in the water.
They are so busy that they have no time to do any sports, ______they need to do so.
I don't know _______.
Hurry up! The train ______. You know it ______ at 8:30 am.
The head teacher insisted that every minute ______ made full use of ______ for the mid-exam.
Hangzhou marathon is a race _______aim is to help people know the importance of taking exercise.