BY THE TIME I APPLIED, ALL THE HOLIDAY VOUCHERS ... USED UP. A. HA...

15. - BO DE KIEM TRA TRAC NGHIEM TIENG ANH T3 5231
BO DE KIEM TRA TRAC NGHIEM TIENG ANH T3 5231

15. By the time I applied, all the holiday vouchers ... used up.

a. had been

b. have been

c. was

d. are

→a