Pollution is a serious problem. Scientists have _____ some good ways to save it.
Let’s go ____ the road. The shop is ____ the other side.
Only four days remained ____ the exam.
Be careful when you go ____ the street because the traffic is very busy at the moment.
–When do you usually get up, Xiaoli? –____ 6:30 in the morning.
The engineer will return from Macao ____ a few days.