1.       I think ____ universe will benefit human beings in the long run.

A.     explore       B. exploring        C. exploration        D. explored

2.       ____ what they have seen, they build a theory about the way in which things happen.

A.     Explaining    B. Explain          C. Explanation        D. To explain

3.       The luggage was so heavy ____ that he had to have it ____ by two strong men.

A.     to carry, carried                 B. to be carried, carried

C. to carry, carry                    D. to be carried, carrying