Today's lesson(I wanted to say...but I couldn't. )

Are these sentence correct?
If there are mistakes, please correct them.
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I think some people drink from the morning,but it's rarely things.
I think some people start drinking in the morning, but it's rare.

I am so bad at math, but I like it. I like it in part of theory.
I'm bad at math, but I like it. I like the theory part of math.

I think we can explain about whole world only by using math theory.
I think we can explain many things about the world by only using math theories.

I studied chemistry but after graduating, I work noting about chemistry, so I forget all.
I studied chemistry, but after graduating since I didn't work in the field of chemistry, I forgot everything.

:)