能得到最纯免疫原的纯化方法是()
A．亲合层析法
B．凝胶过滤法
C．离子交换层析
D．盐析沉淀法
E．超速离心法
参考答案：A
—Did you find the missing couple in the mountain yesterday?
—No, but we ______ to get in touch with them ever since.
A．had tried
B．have tried
C．have been trying
D．had been trying
毒性剧烈、治疗剂量与中毒剂量相近，使用不当会致人中毒或死亡的药品是( )
A．戒毒药品B．麻醉药品C．精神药品D．放射性药品E．医疗用毒性药品
