来料突然中断，各级旋风筒温度（）
A、急剧升高
B、急剧降低
参考答案：A
The student sat there, __________ what to do. [ ]
A. doesn't knowing
B. didn't knowing
C. not know
D. not knowing
维生素B12在胃肠道的吸收部位是（）。
A.回肠
B.十二指肠
C.空肠
D.结肠
E.胃
