THE AIR-HOSTESSES WERE BEGINNING ...OUR LUNCH WHEN THE PLANE BEGAN...

21. - KIEM TRA 1 TIET SO 1
KIEM TRA 1 TIET SO 1

21. The air-hostesses were beginning ...our lunch when the plane began to shake .

A.serving

B. to serve

C. to have

D. A&B are right