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Radium salts, which have been found to _____ in bones, give rise to cancers of the bone.

　　A. pile up    B. build up    C. keep up    D. pull up

Radium salts, which have been found to _____ in bones, give rise to cancers of the bone.

             A. pile up       B. build up      C. keep up      D. pull up

Radium salts, which have been found to _____ in bones, give rise to cancers of the bone.

　　A. pile up    B. build up    C. keep up    D. pull up

Radium salts, which have been found to _____ in bones, give rise to cancers of the bone.

A. pile up    B. build up    C. keep up    D. pull up

Radium salts, which have been found to _____ in bones, give rise to cancers of the bone.

　　A. pile up 　　 B. build up　　 C. keep up 　　 D. pull up