As the plane circled over the airport, everyone sensed that something was wrong. The plane was moving unsteadily through the air, and although the passengers had __21__ their seat belts, they were suddenly thrown forward. At that moment, the air-hostess appeared. She looked very pale, but she was quite 22 . Speaking quickly but almost in a whisper she __23__ everyone that the pilot had fainted and asked __24__ any of the passengers knew anything about machines -- or at least how to drive a car. After a moment's hesitation, a man got up and followed the stewardess into the pilot's cabin.
25 the pilot aside, the man took his seat and listened carefully to the urgent instructions that were 26 by radio from the airport below. The plane was now dangerously close to the ground, but to everyone's relief, it soon began to 27 . The man 28 circle the airport several times in order to become 29 the controls.
Following instructions, the man guided the plane towards the airfield. It shook violently as it touched the ground and then moved rapidly across the field, but after a long 30 it stopped safely. Outside, a crowd of people who had been waiting anxiously rushed forward to congratulate the pilot on a perfect landing.

A.if

B.whoever

C.what

D.how