Using before or before of..........

Hey, How is everything?. I was learning something about grammar and I have learnt to use before and before of.

You must use before when you use a verb in the same phrase:

I studied english becouse my teacher teach me.

If you use a noun you must use before of:

I studied english becouse of my teacher.

Other examples.

I went to buy suggar becouse I want to drink tea

I went to buy suggar becouse of tea

My sister was ill becouse she ate in Mc Donald

My sister was ill becouse of Mc Donald

See you soon.