himba

答案C 的问题出在时间的修饰上。inactive until the embroy cell become irreversibly committed to their final function 。
until the embroy cell become irreversibly committed to their final function是不对的。when the egg is fertilized,the substances become active and,。。。。
不是胚胎发育到不能改变命运的地步，而是刚有胚胎就已经 active。