Swimmers must be very strong in order to build up speed because of the high resistance of

问题补充：

Swimmers must be very strong in order to build up speed because of the high resistance of the water. Runners, , must struggle against the heavy resistance of the air and ground.

A. generally

B. similarly

C. naturally

D. probably

答案：

A. generally

(答案→)B. similarly

C. naturally

D. probably

解析：游泳者与赛跑者相比较，有相似点，故选B。