He was puzzled by this phenomenon. He began to try every approach the best way of working it out.
A. known to find
B. knowing to find
C. known finding
D. knowing finding
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(答案→)A. known to find
B. knowing to find
C. known finding
D. knowing finding
解析：第一题选A ，原因是这里面的known 是做形容词，被知晓的。形容approach方式途径。后面的to find 接目的状语，表示目标。
B knowning 动名词一般是主动意思，所以不正确。
C D不能表示目的含义。