Can the present tense be used in the past tense to refer to something that always happens or to something that hasn't happened yet?

I'm new here so please excuse me if this question's already been asked, I just couldn't seem to find it anywhere.

What I want to know is, can the present tense be used in the past tense?
Let's say I'm in school, and my teacher asks " Why do people cry?". What would be the correct way to write that in the past tense? "My teacher asked why people cried" or, "My teacher asked why people cry"? I've heard of backshifting, but I'm not sure if this is it. I've only recently started worrying about this, and now I feel like I have to contemplate every sentence before I say anything. Please help me if you can. I'm sorry if I seem ignorant, it's my first time using this kind of website.