An adjective clause can identify a noun. The clause comes right after the noun.Basic Patterns for Prepositions in Adjective Clauses: A. TO IDENTIFY A PERSON, AN ADJECTIVE CLAUSE CAN BEGIN WITH WHO(M), THAT, OR Ø:

person             +    introduction     +    adjective clause

subject   +    verb (object)    +    preposition

The man                 who(m)                   she               writes                     to

The man                 that                         she               writes                     to

The man                 —                           she               writes                     to

The people             who(m)                   we                 live                        with

The people             that                         we                 live                        with

The people             —                           we                 live                        with

The doctor             who(m)                   I                    ask                        for

The doctor             that                         I                    ask                        for

The doctor             —                           I                    ask                        for

Make sure the adjective clause is right after the noun:    

The man who(m) she writes to       is my father.

The people that we live with           are nice.

The doctor I always ask for            isn't here.

My father is                                    the man who(m) she writes to.

I really like                                     the people that we live with.

This is not                                      the doctor I always ask for.

    B. TO IDENTIFY A THING, AN ADJECTIVE CLAUSE CAN BEGIN WITH THAT OR Ø.       

thing               +    introduction     +    adjective clause

subject   +    verb     +    (object)      +    preposition

the book                that                         I                    paid ten dollars                    for

the book                —                           I                    paid                                    for

the house               that                         they              are looking                          at

the house               —                           they              are looking                          at

the cities                that                         we                 work                                    in

the cities                —                           we                 work                                    in

    Be sure to put the adjective clause directly after the noun.         

The book that I paid ten dollars for            is great.

The house they are looking at                    is expensive.

The cities that we work in                           are far apart.

  I really like                    the book I paid ten dollars for.

 They might buy            the house they are looking at.

 We love                        the cities we work in.

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