过滤器主要有（）；（）；筛网式过滤器三种类型。
参考答案：水砂分离器；砂石过滤器
—Where is Lucy?
—I can’t say where she is, but she have gone to meet her classmates, for
they want to go to Sichuan to work as volunteers.
A．can
B．should
C．must
D．may
胰腺癌治疗首选的方法是
A．手术治疗B．放疗C．化疗D．免疫治疗E．基因治疗
