单选题 Jupiter ______ perhaps the most important planet of the solar system.
A. was B. were
C. is D. will be

【正确答案】 C
【答案解析】[解析] 结构识别
这是最基本的S+V+P(主系表结构)，此处缺少系动词，因主语是第三人称单数，所以答案为C。