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

Though my grandfather is in his eighties, he is still as _________ as a young man and hates sitting around doing nothing all day.

Mr. Smith has ___collection of coins than anyone else I have ever met.

I am rather      about the full mark that he got in the recent English test, because he never studies.

Overpopulation is a terrible threat to the human race.Yet it is probably ____ a threat to the human race than environmental destruction.