Radium salts，which have been found to in bones，give rise to bone cancer.
A. pile up
B. build up
C. keep up
D. pull up
网友回答
A. pile up
(答案→)B. build up
C. keep up
D. pull up
解析：考查短语辨析。build up(=accumulate) 积累。pile up 堆积。keep up 保持，维持。 pull up 停车。根据句意选B。