题目

某种狗的毛色受到独立遗传的两对等位基因控制：黑色（G)对棕色（g)为显性；颜色表达（H)对颜色不表达（h)为显性，无论黑色或棕色基因是否存在，只要颜色不表达基因存在，狗的毛色为黄色。某人让一只棕色公狗与一只黄色母狗交配繁殖多次，后代中三种颜色的狗都有一定数量。据此分析，下列叙述正确的是（ ）A.两只亲代狗可为纯合子，也可为杂合子B.F1中棕色狗基因型种类与黑色狗一样多C.F1中出现黑色狗是基因突变的结果D.F1中黄色狗都为纯合 John is the tallest boy in the class, _______ according to himself. A. five foot eight as tall as            B. as tall as five foot eight C. as five foot eight tall as            D. as tall five foot eight as