题目

Once there was a huge apple tree．A little boy loved to come and play around it every day．He loved the tree and the tree loved to play with him．Time went by---the little boy had grown up and he no longer played around the tree every day．One day, the boy came back to the tree and he looked sad．“Come and play with me, ” the tree asked the boy．“I'm no longer a kid．I wouldn't play around the tree any more．” the boy replied．“I want toys．I need money to buy them．” “Sorry, I don't have money．But you can pick all my apples and sell them．So, you will hav15、14.右图所示的遗传系谱图中，2号个体无甲病致病基因。1号和2号所生的第一个孩子表现正常的几率为 A．1/3            B．2/9        C．2/3             D．1/4