The rooms in the apartment buildings were______.
A. small and crowded
B. clean and tidy
C. bright and sunny
D. tall and big
在其他条件相同的情况下,抽样误差较小、样本代表性较好的抽样方法是_______。
A. 纯随机抽样
B. 机械抽样
C. 类型抽样
D. 整群抽样
当有用信号的频率低于100 Hz时,应采用__________滤波电路。
A. 低通
B. 高通
C. 带通
D. 带阻
How much does it cost for five stamps?
A. 20 cents.
B. $1.00
C. $2.20.