专升本考试

【单选题】 Scientists ______that bacteria through microscopes for many years．
A．studied
B．have studied
C．had studied
D．have seen studied

网考网参考答案：B
网考网解析：
[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。 查看试题解析出处>>