I would have gone with you but I have to prepare for an exam.

我本要和你一起去，但我不得不准备考试。

youdao

One day I hurried home for lunch after school, because there would be an exam in the afternoon and I had expected to go back to school early to prepare for the exam.

一天放学后我匆忙回家吃午饭，因为下午考试，我希望早一点回校准备考试。

youdao

The best I could do was to share with him that the average time to prepare for such an exam was three months or more, with a committed study time of an hour a day or more, then I wished him good luck.

我能做到最好的，就是跟他分享，最佳的准备此类考试的时间是三个月，或者更多，每天坚持有一个小时或以上的学习时间，然后我就祝福他好运了。

youdao