BY 1877, THE FIRST TELEPHONE WAS ON COMMERCIAL USE. A B C D A B C...

16. - DE KIEM TR 1 TIET KHOI 8 CO DAP AN 16. - DE KIEM TR 1 TIET KHOI 8 CO DAP AN
DE KIEM TR 1 TIET KHOI 8 CO DAP AN

16. By 1877, the first telephone was on commercial use.

A B C D

(17-20) Give the correct form of the verb: (1,0pt)