When changing lanes, a driver should use his turning signal to let other drivers know ______.

A．he is entering which lane

B．which lane he is entering

C．is he entering which lane

D．which lane is he entering

下颌骨的薄弱部分为

A．正中联合
B．颏孔区
C．下颌角
D．髁状突颈部
E．喙突