Core concept: 虚拟语气结构。 解题思路: Subjunctive requires base verb form. 选项分析: D. Uses 'be' correctly (proper mandative subjunctive). A. Incorrect 'was' (should be 'were'). B. Missing past perfect ('had...would have'). C. Wrong indicative 'arrives' (should be 'arrive'). 易错点: Overlooking verb form requirements.