Only a small part of the energy of the sun___by man so far.
Only a small part of the energy of the sun___by man so far.
A.has been used
B.was used
C.has used
D.will be used
属于什么语法时态?
A.has been used
B.was used
C.has used
D.will be used
属于什么语法时态?
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