第3题: [单项选择]有350个人,不是研究生就是本科生,从中任取一人,问是女研究生的概率为多少 (1)研究生有187 (2)女生有247 A. 条件(1)充分,但条件(2)不充分. B. 条件(2)充分,但条件(1)不充分. C. 条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来充分. D. 条件(1)充分,条件(2)也充分. E. (E) 条件(1)和条件(2)单独都不充分,条件(1)和条件(2)联合起来也不充分. 参考答案:E
第18题: [单项选择]Scientists ______that bacteria through microscopes for many years. A. studied B. have studied C. had studied D. have seen studied 参考答案:B 答案解析:[解析] 本题考查时态的用法。由于句中已有“for many years”,故应用现在完成时。