It can be learned from Paragraph 3 that the public-sector unionization is______.
A. currently compulsory but beneficiary
B. beneficiary but not necessary
C. optional but popular
D. voluntary but ignored
查看答案
The word signaled in paragraph 4 is closest in meaning to
A. followed
B. announced
C. concluded
D. delayed
The distribution pattern of individuals within a population's geographical boundaries is known as
A. population ecology
B. population density
C. population change
D. population dispersion
Why does the author compare books with radio technology in paragraph 5？
A. To describe the influence of handwritten books on radio
B. To explain how both changed patterns of information flow
C. To show that both were initially confined to a few users
D. To complain about the social restrictions imposed on radio
The word those in paragraph 6 refers to
A. walls
B. roofs
C. huts
D. features
微信支付 
支付宝支付