Most air pollution is caused by the burning oflike coal, gas and oil.
. Why __________ put the meat in the fridge ? It’ll stay fresh for several days.
. I wonder how he could __________ not handing in his maths exercises yesterday, for his maths teacher is always strict with his students.
. She was educated at Beijing University, __________ she went on to have her advanced study abroad.
. --- Can you read the sign , sir ? No smoking is allowed in the lift ! --- __________.
. Tom is reading a book __________ his brother is watching TV.