APA

Williams M., . (2011). Challenges 2. Essex: Pearson Education Limited.

Chicago

Williams Melanie, . 2011. Challenges 2. Essex: Pearson Education Limited.

Harvard

Williams M., . (2011). Challenges 2. Essex: Pearson Education Limited.

MLA

Williams Melanie, . Challenges 2. Essex: Pearson Education Limited. 2011.