Much progress ________in telecommunications during World War I, but the basic technique________in the previous decades. A. was achieved - had been developed B. has been achieved - were developed C. had been achieved - has been developed D. would have been achieved - were developing - Tenses | English Grammar Quiz

Much progress ________in telecommunications during World War I, but the basic technique________in the previous decades.

A. was achieved – had been developed

B. has been achieved – were developed

C. had been achieved – has been developed

D. would have been achieved – were developing

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