问题描述：
[单选]
The vacuum tube， invented near the beginning of our century， gave us the use of radio waves， an energy source never before（）and later opened the road for television．
A．was captured
B．captured
C．capturing
D．has been captured
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答案解析：无
答案解析：无
上一篇：The Great Depression was the longest and most severe period of economic depression（）the United States．
下一篇：Television is an instrument of communication，（）us to see us as well as to hear the performer．
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