However, in recent years, Niagara Falls have e to be appreciated more for their natural beauty as wonder of nature.
A. 不填; a
B. the; the
C. 不填; the
D. the; a
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(答案→)A. 不填; a
B. the; the
C. 不填; the
D. the; a
解析：in recent years近年来；a wonder of nature自然界的一个奇迹。