Question

—（？）—, we would have finished the work on time.选Had Jim come的原因

Answer 1

这是一个虚拟语气强调句。
原句应该是：If Jim had come, we would have finished the work on time.
意思是强调过去某个时间，如果Jim来了，我们就会按时完成工作。隐含的意思是：实际上由于他没有来，工作没有完成。
作为强调句的时候，谓语助动词提前。