For those who work with their brains, exercise is .
A. of very value
B. of great valuable
C. great valuable
D. very valuable
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A. of very value
B. of great valuable
C. great valuable
(答案→)D. very valuable
解析： 考查形容词作表语。Great修饰名词，very修饰副词；排除A,C；B项应把valuable换成value，所以选D。