NOW, IT´S TIME TO PRACTISE
I highly recommend you to visit these links to practise Relative Clauses on the web.
Defining relative clauses 1
http://www.perfect-english-grammar.com/relative-clauses-exercise-1.html
Defining relative clauses 2
http://www.perfect-english-grammar.com/relative-clauses-exercise-2.html
Defining relative clauses 3
http://www.perfect-english-grammar.com/relative-clauses-exercise-3.html
Defining relative clauses 4
http://www.perfect-english-grammar.com/relative-clauses-exercise-4.html
DEFINING - NON DEFINING RELATIVE SENTENCES