1Alexander L G. Look, Listen and Learn [M] . London: Longman, 1968.
2Svartvik J, Ekedahl O. Verbs in public and private speaking. In: Aarts B, Meyer C F. (eds.) . The verb in contemporary English: theory and description [M] . Cambridge: Cambridge University Press, 1995 : 273-289.
3Blum-Kulka S, Levenston E A. Universals of lexical simplification [J] . Language Learning, 1978 (28): 399--416.
