However, at times this balance in nature is disturbed, ____ a number of possibly unforeseen effects.

1___ old man is ____ teacher. He likes playing ____basketball after supper.

Mary kept weighing herself to see how much ______ shewas getting.

The question is not easy, so________ students can answer it.

What are you going to do tonight— ______. If I am free, I may go to the cinema with my mother.