单选题
If 
of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes?
of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes?
【正确答案】
A
【答案解析】[解析] 因为每次抽出容器中空气的
，所以4次柚出的空气与原始空气的比分别为
，其和为：
，所以4次柚出的空气与原始空气的比分别为，其和为：