单选：《宋论》对宋初政事的总体评价是（）A．管理混乱B．散漫无章C．张弛有度D．酷刑严厉

I can’t finish the task within 1 hour.

He failed to live up to his parents' expectations.

Everything considered, their plan is still workable.

先天缺额牙最多发生在（）。A．上颌侧切牙B．上颌第二前磨牙C．下颌第二前磨牙D．上下颌第三磨牙

简述闭口肌群的组成及功能。