题目内容
(2006·上海)
Black holes ________ not be seen directly, so determining the number of them is a tough task.
[ ]
A．can
B．should
C．must
D．need
答案：A
练习册系列答案
新思维假期作业寒假吉林大学出版社系列答案
相关题目
In an hour, we can travel to places _______ would have taken our ancestors days to reach．（2006上海卷）
|
A．where |
B．when |
C．which |
D．what |