SAT中which用法问题Princeton Review 上一题Many citizens rush to fill

SAT中which用法问题
Princeton Review 上一题
Many citizens rush to fill out their tax returns the night before the deadline,(which leads t o careless mistakes.)答案说是错的解释是which跟deadline,会误解为修饰deadline.
答案选;rushing can lead to careless mistakes.
但同样是Princeton,另一题
Final exams were incredibly (comprehensive and went on for two weeks,which made) it seem as if they would never end.
这里的which却是对的.我觉得两个which都指的是当做整体的“一件事”,也都有逗号隔开,为什么前面不对后面对呢?SAT里which能否指代前面整件事要怎么判断呢?