答案：B

题目分析：句意：如果今天是星期天，我将不去上学。 虚拟语气用于条件状语从句中，可以表示与现在事实相反的假设，条件状语从句中的谓语动词用“过去式（be动词用were）”，而主句中的谓语动词用“would / should/ could / might + 动词原形”。如：1.If I were you, I would join the army. 2.If she had time, she should go with you.。由句意可知选B。

考点: 考查虚拟语气的用法。