Question

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

Answer 1

C

考查動詞的用法。句意“晚上熬夜對健康有害。”句子缺少主語，而動詞原形不能作主語；動名詞可以作主語，作主語時，謂語用單數。故選C。