分泌的消化液不具有消化酶的消化腺是 [ ]
A．唾液腺
B．肝脏
C．肠腺
D．胰腺
答案：B
It's a very difficult question , so ______of the students could answer it [ ]
A. none
B. all
C. every
D. some
比较筒式钢球磨、中速磨与风扇磨对煤种的适用条件有什么不同？
