Gilbert, J. B. (2005). Clear speech: Pronunciation and listening comprehension in North American english teacher`s resource book (3rd ed.). Cambridge University.

Gilbert, Judy B. Clear Speech: Pronunciation and Listening Comprehension in North American English Teacher`s Resource Book. 3rd ed. Cambridge: Cambridge University, 2005.

Gilbert, Judy B. Clear Speech: Pronunciation and Listening Comprehension in North American English Teacher`s Resource Book. 3rd ed. Cambridge University, 2005.