I always wanted to do the job which I'd been trained _____.[ ]
A. on
B. for
C. by
D. of
答案:B
某中学在高一开设了数学史等4门不同的选项修课,每个学生必须选项修,且只从中选一门.该校高一的3名学生甲、乙、丙对这4门选课的兴趣相同,则3个学生选择了3门不同的选修课的概率是 ______.
病毒复制过程中可产生RNA-DNA杂交体的是()
A.+ssRNA病毒
B.dsRNA病毒
C.dsDNA病毒
D.逆转录病毒
E.一ssRNA病毒