口腔颌面部感染的主要途径是（）
A.牙源性感染
B.腺源性感染
C.损伤性感染
D.血源性感染
E.医源性感染
参考答案：A
在日常生活中，人们常根据敲打物体发出的声音来鉴别物质，以下做法中用以达到这一目的是（ ）
A．瓜农用手拍打西瓜
B．铁匠用小锤敲打烧红的铁块
C．瓦匠用瓦刀敲打砖
D．自行车上敲击车铃
Have you ever met with this case in your life________you can't understand others even if they have
said something several times?[ ]
A. where
B. what
C. that
D. which
