20世纪初期,抽样方法逐渐发展起来,与()和()结合在一起,形成抽样调查,成为现代社会调查研究的主要标志.
参考答案:问卷法;统计分式
Lucy: Does Aunt Tara enjoy ?
Mark: Yes. She has three dogs, two rabbits, four birds, and some fish in her house.
A.collecting dolls
B.keeping pets
C.visiting the zoo
D.working on the farm
脉冲库顶除尘器装于灰库顶部,用于灰库()之用,保证排气无粉尘。