Study the voiceless/voiced pairs on page 150 of your Well Said Intro book.
Matching quiz on Thursday.
See Link for more examples:
http://www.elearnenglishlanguage.com/esl/pronunciation/consonantsvoiced-unvoiced.html
ISBN Numbers for Well Said Intro CDs: (If you want to order the CDs)
ISBN-13:978-1-4130-0716-9
ISBN-10:1-4130-0716-3