http://books.google.com/books?id=XFGo73bIaNkC&pg=PA15&lpg=PA15&dq=patterns+for+a+purpose+topic+sentence&source=bl&ots=qFrPSI3lwK&sig=h9-ufWkERUIPU7AxrPlaSvLGLOo&hl=en&ei=YZT2Tdv6NYOWsgP9rIjdBw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBYQ6AEwAA#v=onepage&q=patterns%20for%20a%20purpose%20topic%20sentence&f=false

http://www.laflemm.com/dynamic/online_practice.php?practice_id=19

http://owl.english.purdue.edu/owl/resource/606/01/

http://academic.cuesta.edu/acasupp/as/308.HTM