SINCE 1980, SCIENTISTS IN THE WORLD A LOT OF THINGS TO FIGHT AIDS....

24. - TRAC NGHIEM TA 12 UNIT 2 KEY
TRAC NGHIEM TA 12 UNIT 2 KEY
24. Since 1980, scientists in the world a lot of things to fight AIDS.

A.

have done B. did C. are doing D. had done