it is required to follow the grammatical ruled when witting English,there are always some exceptions.
A. Unless
B. while
C. As
D. Since
网友回答
A. Unless
(答案→)B. while
C. As
D. Since
解析：根据句子逻辑，该从句应该是让步状语所以选择表示“虽然，尽管”的while。本句意思是：虽然在写作时有很多语法规则要遵从，但也总是有一些例外。
【标签】状语从句