题目

I often see him______________ with his dog in the park. A . play B . plays C . to play D . played 答案：A某个DNA片段由500对碱基组成，A+T占碱基总数的34%。若该DNA片段复制2次，共需游离的胞嘧啶脱氧核苷酸分子个数为 A．330        B．660        C．990       D．1320