Question

13. Life is like riding a bicycle.     your balance, you must keep moving.

A. Keeping       B. To keep

C. Keep       D. Having kept

Answer 1

13.   B考查不定式短语作状语。句意：生活就像骑自行车。为了保持平衡，你必须继续前进。根据must keep moving可知，目的为保持平衡，表示目的用不定式。故选B。