【题目】A recent research shows that there _____ volcanic activities on the moon and Mars. However, they no longer exist now.
A. had been B. has been C. were D. would be
在线课程【答案】C
【解析】
试题分析：考查时态。根据下文的However, they no longer exist now.可知，现在它们不再存在了，故可以判断是曾经存在，故使用一般过去时，选择C。句意为：最近的研究表明在月球和火星上曾经有火山运动。