Concept:The word "besides" means "in addition to".
It is used when one person does more than one activity or teaches more than one subject.
Explanation:The sentence means the teacher teaches English and also teaches maths.
So, the correct expression is: Our teacher teaches English besides maths.
"Besides" correctly shows that English is taught in addition to maths.
"Beside" means "next to", so it is incorrect here.
"With" would sound unnatural because it does not join two taught subjects correctly.
"Both" would need the word "and": "both English and maths".
Hence, only option D fits grammatically and logically.
Answer:D. besides