regular exercise is very important, it is never a good idea to exercise too close to bedtime..
A. If
B. As
C. Unless
D. Although
网友回答
A. If
B. As
C. Unless
(答案→)D. Although
解析：考察连词辨析。A如果；B随着；C除非，如果…不；D即使，尽管；句意：尽管经常锻炼很重要，但是锻炼到睡觉的时候却不是一个好主意。根据句意说明上下文是转折关系，故D正确。