Bicycling is a good exercise; it does not pollute the air.A. besidesB. besideC. thereforeD

问题补充：

Bicycling is a good exercise; it does not pollute the air.

A. besides

B. beside

C. therefore

D. otherwise

答案：

(答案→)A. besides

B. beside

C. therefore

D. otherwise

解析：句意：骑自行车除了不污染空气外还是一种很好的锻炼。besides除……外（包含在内）， B.beside在附近C.therefore 因此 D.otherwise否则，故选A。