Scientists study ____ human brains work to make computers.
What worried the woman most was ______ to visit her sick son in hospital.
The thief used a ladder that had been ______ by some workmen, and climbed over the wall.
—Hi, what did our monitor say just now?—Every boy and every girl as well as teachers who are to visit Water Cube asked to be at the school gate before 6∶30 in the morning.
When I entered the room, I found Mary ______ at the desk ______ her homework.
Yesterday we visited a modern hospital, around _________ some fruit shops.