题目

牵牛花的叶子有普通叶和枫形叶两种，种子有黑色和白色两种。现用普通叶纯种白色种子和枫形叶纯种黑色种子作为亲本进行杂交，得到的F1为普通叶黑色种子，F1自交得到F2，结果符合基因的自由组合定律。下列对F2的叙述错误的是( ) A．F2中有9种基因型，4种表现型 B．F2中与亲本表现相同的个体大约占3/8 C．F2的普通叶白色种子中纯合子占1/16 D．F2中普通叶与枫形叶之比为3∶1  --- What were you and your cousin doing at this time yesterday?--- He was reading a magazine ________ I was writing an e-mail.A. as B. while C. when D. after