the situation, Charles Yerkes undertook the system in 1902 by obtaining ownership of many different lines.
A. Seeing, improving
B. Seen , improved
C. To see, to improve
D. Having seen, improving
网友回答
A. Seeing, improving
B. Seen , improved
C. To see, to improve
(答案→)D. Having seen, improving
解析：考察分词作状语和固定搭配。第一空的动词see与句子主语Charles Yerkes构成主动关系，说明使用现在分词，因为这是已经发生的事情，故使用完成式。第二空是固定词组undertake doing sth承诺做某事。故D正确。