蛋白酶按其降解多肽的方式可分为（）和端肽酶两类，其中端肽酶又可分为羧肽酶和氨肽酶。
参考答案：内肽酶
The farmers ________ on the farm when a UFO flew over their heads. [ ]
A. worked
B. work
C. are working
D. were working
不属尿路感染易感因素的是()
A．尿路梗阻
B．糖尿病
C．长期保留导尿
D．附睾炎
E．外阴皮肤慢性炎症
