Sharpe, P. J. (1994). Pass key to the TOEFL iBT: Test of English as a foreign language : internet-based test (6th ed.). United States of American: Barron's Educational Series, Inc.

Sharpe, Pamela J. Pass Key to the TOEFL IBT: Test of English As a Foreign Language : Internet-based Test. 6th ed. United States of American: Barron's Educational Series, Inc, 1994.

Sharpe, Pamela J. Pass Key to the TOEFL IBT: Test of English As a Foreign Language : Internet-based Test. 6th ed. United States of American: Barron's Educational Series, Inc, 1994.