19. Victoria _____ for half an hour when the doctor finally arrived.
a)has been waiting
b)had been waiting
c)was waiting
d)has waited
20.Anita _____ very hard at the moment.
a)is studing
b)studies
c)studied
d)has studied
Trong câu có at the moment nên chia ở thì hiện tại tiếp diễn .
Cấu trúc :
S + is/are/am + V_ing + O