relative clause exercise

a. 'who' is used to refer to persons by stating what the person(s) does / do.

eg: The man who robbed you was arrested by the police yesterday.

b. 'whom' is used to refer to persons through another action done by a different subject.
(When the relative pronouns are the object (receiving the action) of the dependent clause, use 'whom')

eg: The student whom the teacher had praised finally won the competition.
eg: The most popular karaoke song request is "The girl ..... I marry".
We can use whom to refer to girl as this is the object of the relative clause.

see more: http://grammar.uoregon.edu/pronouns/relative.html

good