Have you realized the difficulty we have ____ the problem?

___________ is it from Suzhou to Beijing?— It used to be a long way, but nowadays, it takes only five hours to get there by high-speed rail.

Kate dances so well. Has she ever been trained? –No. He learns all by herself. She ______ goes to any training class.

Our teacher said there would be ______ books in the new library.

There is ___________ “s” and __________ “u” in _______word “student”.