several times, the young scientist still kept on doing his experiments.
A. Having failed
B. Having been failed
C. Failed
D. To fail
网友回答
(答案→)A. Having failed
B. Having been failed
C. Failed
D. To fail
解析：考查分词做状语。本题的fail与句子的后足浴the young scientist之间构成主动关系，故使用现在分词的形式。因为多次失败是在谓语动词之前就发生的，所以使用完成式。句意：已经多次失败，这个年轻的科学家仍然还在坚持做实验。故A正确。