Mr. Wang made up his mind to devote all he could his oral English before going abroad .A.

问题补充：

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

答案：

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。