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It was not until 1920 _______ regular radio broadcasts began.

A. while　 　B. which　　 C. that　 　　D. when

It was not until 1920 ________ regular radio broadcasts began.

A. while　 B. which　 C. that　　 D. since

It was not until 1920 ______ regular radio broadcasts began.

A. while　　　       B. which　　　　    C. that　　　　       D. since　　  　　

It was not until 1920________ regular radio broadcasts began.

A. while　　　　　　　　　　    B. which　　　　　　　　　　    C. that　　　　　　　　　　    D. since

A. while　　　　　　　　　　    B. which　　　　　　　　　　    C. that　　　　　　　　　　    D. since