Which of the following best reveals the main idea of the passage？
A. Surprising discoveries of new species are commonplace.
B. The mystery of the deep sea and the soil remains to be uncovered.
C. Knowledge of global species diversity is still limited.
D. Estimates of global species diversity vary among scientists.
查看答案
What is e-mail？
A live conversation with an expert.
B. A means of communication.
C. A long-distance call service.
D. A mail delivery system.
A．withB．byC．withoutD．from
A. with
B. by
C. without
D. from
A．askB．doubtC．careD．wonder
A. ask
B. doubt
C. care
D. wonder
The second book was ______ by August, but several months later, its publication was still
A. completed
B. to complete
C. to have completed
D. to have been completed
微信支付 
支付宝支付