Why pleasant smells do not reduce pain in man is a question still by scientists.
A. answered
B. being answered
C. to be answered
D. that answered
网友回答
A. answered
B. being answered
(答案→)C. to be answered
D. that answered
解析：考查非谓语动词。句意：为什么令人愉快的气味不能降低人的痛苦仍是科学家要回答的问题。根据语境看问题还没被解决所以用不定式的被动式做a question的定语。