_____ of their bad habits, the boys switched from being dependent on their parents to _____ for others.
—Could we go and visit the Summer Palace?—Yes,________.This should be on our list of things to do in Beijing.
It's OK to________an electrical appliance on so long as you are using it.
It________heavily for 2 weeks and the farmers were very worried.
You cannot tell________looking at someone whether or not he has HIV.
The days are gone________you can breathe fresh,unpolluted air or drink clean, unpolluted water in the countryside.