Although many modifications have been made in it, the game known in the United States as football can be traced directly to the English game of rugby.

A．rules

B．changes

C．demands

D．leagues

右图是一个人类白化病遗传的家族系谱。6号和7号为同卵双生，即由同一个受精卵发育两个个体。8号和9号为异卵双生，即由两个受精卵分别发育而成的两个个体。

6号是纯合子的几率是（），9号是杂合子的几率是（）