Question

      up late at night is bad for our health.
A Stays     B .Stay C. Staying

Answer 1

C

考查动词的用法。句意“晚上熬夜对健康有害。”句子缺少主语，而动词原形不能作主语；动名词可以作主语，作主语时，谓语用单数。故选C。