He had to pause from time to time to wipe the sweat from his forehead, because the airconditioningsystem ________. [ ]

Which subject is _____ ， physics or chemistry

What do you enjoy most in life? — _______ time with good friends. It’s really good fun. [ ]

How can you manage to do all these things without a rest-I prefer_______ a cup of coffee_______ me energetic.

8, three American scientists invented ____transistor, which is ____ small electronic device to control an electriccurrent