How to ask "Is it because..." questions
In fact this is a sentence that enhances the reason why……? And now you can reguard it in English, something like:

It's because I saved a sick man that I was late for school……

To translate this into Chinese directly, this means：是因为AA，所以导致BB的后果。

(Change this to English in question：Is it because you saved a sick man that you were late for school?)

To translate this into Chinese directly, this means：是因为AA才导致BB吗？

In Chinese, we always ignore something according to the actual context, and such statement as this always happens when a teacher see that you are late for school, and maybe the student will make a dialog like this:

Teacher: Why are you late for school?

Student: It's beause I saved a sick man (that I was late for school). 

Teacher: Really？Is it because you saved a sick man (that you were late for school)?

是真的吗？是因为你救了一个病人（以至于你上学迟到了？）