Mr. Wang made up his mind to devote all he could his oral English before going abroad .
A. improve
B. to improve
C. improving
D. to improving
网友回答
A. improve
B. to improve
C. improving
(答案→)D. to improving
解析：考查动词短语。本题考查动词短语devote … to (doing)…致力于、专心于……，to为介词。句意：王先生下定决心在他出国之前全身心于提高他的口语。根据句意说明D正确。