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

问题补充：

up late at night is bad for our health.

A Stays B .Stay C. Staying

答案：

解析：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。