Which conjunction correctly introduces a reason in this sentence: 'Journals need stricter policies, _____ many studies contain statistical flaws'?
答案解析
核心考点：连词逻辑关系。解题思路：后半句是前半句政策严格的原因，'because'表因果关系。错误选项分析：A. but表转折，B. unless表条件否定，D. however需分句结构。易错点提醒：可能误选A，但原句为因果而非转折关系。
正确答案：C