单项选择题

Our airplane was just besides the airport building. It did not look too strong to me, but I decided not to think about such things. We saw the baggage going out 1 it on trolleys and being loaded from 2 the aircraft. Next, three men and three girls, all in uniform, went over to the plane and 3 it. Over the loudspeakers we were 4 the plane was ready to leave and were asked to walk out to it. Everybody moved quickly in order to 5 the seats they wanted. I was 6 to get a seat near the tail, but the plane looked 7 inside than it had from outside. I fastened my seat belt 8 we took off and tried to forget my nervousness.
After an hour"s flying I 9 black clouds ahead through my window. An electric sign flashed 10 : "Fasten your seat belts, please," and one of the hostesses made a similar request over the loudspeakers. She told us we were about to fly into a storm but 11 cheerfully there was nothing to worry about. Suddenly, the plane 12 all over, dropped about twenty feet and seemed to hang on one 13 . Then it rose twenty feet and there was a great flash of lightning. The three girls did their best to 14 pills for airsickness and comfort the passengers. Soon the sky became light again. The pilot had 15 to get above the storm.

A.before
B.after
C.until
D.when