APA

Ashworth J., Clark J., . (1999). Stepping Stones 3. Harlow: Longman.

Chicago

Ashworth J, Clark J, . 1999. Stepping Stones 3. Harlow: Longman.

Harvard

Ashworth J., Clark J., . (1999). Stepping Stones 3. Harlow: Longman.

MLA

Ashworth J, Clark J, . Stepping Stones 3. Harlow: Longman. 1999.