The first laser ------- in 1960 by Maiman almost half ...

[ Grammar ]

The first laser ——- in 1960 by Maiman almost half a century after the publication of Einstein’s theory of radiation which ——- the possibility of laser operation.

A. has been demonstrated / had shown

B. had been demonstrated / showed

C. was demonstrated / showed

D. demonstrates / was shown

E. was being demonstrated / shows

Select your answer:
A B C D E

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