--This kind of sports is exciting.--Yes,but it's dangerous.One can't do it ____ he or she has got some training.
Sam is a little weak in English and he has _____ what the teacher says in class.
______ great fun they had singing and dancing last Sunday night!
Not only you but also he ________ to my birthday party.
The floor requires_________.
I think your advice is of great value to me and it’s well worth ________.