HE ________ THE EFFECTS OF RADIATION WHEN HE SUDDENLY DIED.A. WAS S...

9. - TRAC NGHIEM ON THI TOT NGHIEDE CHNH SUA
TRAC NGHIEM ON THI TOT NGHIEDE CHNH SUA

9.

He ________ the effects of radiation when he suddenly died.

A. was studying

B. studied

C. had been studying

D. had studied