The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

Is it, "Where was the TEACHER?"
The Big Bang Theory Season 11, Episode 13

My apologies, Leonard.
I'm only as good as my TEACHER.
The Big Bang Theory Season 1, Episode 17

high school science TEACHER
Mr. Hubert Givens..."Sheldon, Sheldon.
The Big Bang Theory Season 12, Episode 23

Well, you're a wonderful TEACHER.
Game of Thrones Season 5, Episode 2

With my master, I was a TEACHER.
Game of Thrones Season 4, Episode 10