--Which car is better, the red one or the black one?--I prefer the red one, but it is really a matter of personal________.
I still remember the accident and the troubles ______ has caused to me.
Fujian has shut down the chicken markets ______ human infections of H7N9 were found.
I got to the lecture hall very early, ______ to get a good rest.
It hasn’t been announced ______ the plane is to take off.
Students ______ to do some voluntary work every year.