题型:单项选择题 A1/A2型题 构成传染过程必备的环节是()A.传染源、传播途径、易感人群B.病原体的数量、毒力和机体免疫力C.病原体、人体和病原体所处的环境D.病原体、社会因素、自然因素E.屏障作用、吞噬作用、体液作用 查看答案
题型:填空题 Krashen argues that attitudinal factors also play an important role in acquiring a second language, and this is his ______ hypothesis filter. 查看答案