婴幼儿颌下间隙感染常继发于（）
A.下颌磨牙根尖感染
B.上呼吸道感染
C.医源性感染
D.血源性感染
E.化脓性颌下淋巴结炎
参考答案：E
If you have some questions, please _____. [ ]
A. write down them
B. write them down
C. put them up
D. put up them
—Mum, could I have a MP3 like this?
—Certainly, we can buy _____ one, but as good as this. [ ]
A. a cheap
B. a cheapest
C. a cheaper
D. the cheapest
