单选题 Science fiction stories ______ out-of-date when scientific knowledge the stories are based on changes.
  • A. become
  • B. becoming
  • C. is becoming
  • D. becomes
【正确答案】 A
【答案解析】[解析] 语法：动词形态 1．选项均为动词。 2．句子的主语science fiction stories是复数形式，因此A become为正确选项。