You can use "at which", "in which" and "to which" to mean...
where
who
when
that
Mark, ..... you know, is really into surfing.
who
which / that
who / whose
who / that
Is this sentence correct? "I dislike the characters appear in Harry Potter"
I dislike the characters WHICH / THAT appear in Harry Potter.
Make this sentence more formal: "Nicole is the first girl who I fell in love with"
Nicole is the first girl WITH WHOM I fell in love.
Join the sentences with a relative clause: I visited a graveyard. Elvis is buried there.
I visited the graveyard where Elvis is buried.
"This is the house where I was born" What can replace "where" ?
when
in which
for whom
that
Create a sentence with a relative claude: "This is the medicine. Mark depends on it"
This is the medicine WHICH Mark depends ON .
That's the person ..... dog almost bit me!
whose
who
that
which
Join the sentences with a relative clause: You know David. He is going to Armenia.
David, who you know, is going to Armenia.
Join the sentences with a relative clause: I'm sick. It's because of the water.
The water is why I am sick. / I'm sick, which is because of the water.
My boss with ..... I had argument was really angry.
whom
which
why
when
Join the sentences with a relative clause: James is a teacher. I blame my failures on him.
James is the teacher on whom I blame my failures.
Harry is the singer ..... song went to number one.
whose
who
which
who's
This is the book ..... which the film is based.
ON
The reason ..... I'm late is because of a traffic jam.
why