激活胰蛋白酶原变为胰蛋白酶的主要物质是（）
A．盐酸
B．组胺
C．内因子
D．糜蛋白酶
E．肠激酶（肠致活酶）
参考答案：E
—What are you busy with?
—The conference_________in Meitan next week. [ ]
A. to be held
B. held
C. will be held
D. being held
量油尺的尺锤必须是（）材料。
