EF45 adjective clauses

who
The girl who lives down the street is my friend. SUBJECT PRONOUN

The girl who I walk to school with is my friend. OBJECT PRONOUN, EASIEST, CLEAR

The girl who I walk to school with is my friend. MOST AUTHENTIC

The girl whom I walk to school with is my friend. VERY FORMAL
The girl with whom I walk to school is my friend. VERY VERY FORMAL


which
Ottawa, which is the capital of Canada, is in Ontario. ONLY ONE
My hometown, which is Kaiping, is a big city.
My hometown, where is Kaiping, is a big city. NO!


The apple, which is red, is sweet. SOUND LIKE ONLY ONE

that
The apple that is red is sweet. SOUNDS LIKE SEVERAL APPLES 

whose

where
My hometown, where I was born, is Kaiping.
The house where my sister lives has a leaking roof.
where S V
The SUBJECT, where something happens, VERB.
The school where we study is very old.


"That rings a bell." "I kind of remember that."