c He regretted forgetting (that) it was his mother's birthday and saying Happy Birthday to her这里我们看到AND 前后并列的其实是forget和say.他很遗忘忘记了,忘记了什么?忘记了一件事,用that引导的宾语从句,th...但是it在整句中 替代的是哪个？亲~代替his mother's birthday，作为形势主语