Do you like English？
Yes， but I think____ is a great challenge to learn the language well．（ ）
A．thatB．thisC．it
Could you tell me ______ ？
I'm not sure．（ ）
A．how many people have joined the club
B．when is Thanksgiving Day
C．which animal does he like best
D．what time will the dolphin show start
The gift often reminds me of the days ______ I spent in the countryside．（ ）
A．whatB．thatC．whoD．when
He speaks French well，but of course he doesn't speak_______ a person from France．（ ）
A．as clear asB．clearer than
C．as clearly asD．the more clearly
We _______ the lessons for half a year．We are sure we can make it．（ ）
A．reviewB．reviewed
C．have reviewedD．are reviewing
With the development of science and technology ，5G _____ to help us live more conveniently．（ ）
A．usesB．is usedC．can useD．used