The restriction is somewhat vague and ________ cannot prevent al

The restriction is somewhat vague and ________ cannot prevent all violations.
A、that
B、nevertheless
C、therefore
D、whether
【正确答案】：C
【题目解析】：that引导从句，前面有and，表并列，说明后面不是从句；nevertheless然而；therefore因此；whether是否
句意：这个限制有些模糊，因此不能防止所有的违规。