--Hello, Sandy. This is Jack. What are you doing?---I’m watching a match. It started at 7:00 p.m. and _____ on for another an hour.
_____ the environment is important for human beings.
I can’t stand _____ for you so long.
—Is the bag beautiful? —Yes, at _____ it’s _____ the one you bought for me.
Our teacher told us that light _____ much faster than sound.
In our class _____ of the students _____boys.