Black holes can not be seen directly, so determining the number of them is a___________ task. [ ]A.

题目简介

Black holes can not be seen directly, so determining the number of them is a___________ task. [ ]A.

题目详情

Black holes can not be seen directly, so determining the number of them is a___________ task.  
[     ]
A. rough  
B. strict  
C. tough  
D. firm
题型:单选题难度:中档来源:同步题

答案

C

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