That is secret． ．
A. Only knows Mary how to do it
B. Only does Mary know how to do it
C. Only Mary knows how to do it
D. Mary knows only how to do it
网友回答
A. Only knows Mary how to do it
B. Only does Mary know how to do it
(答案→)C. Only Mary knows how to do it
D. Mary knows only how to do it
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