Emilie; Polonsky, Jonathan Aaron; Ryan, Michael J.; Touré, Alhassane; Towner, Rodney; Tshapenda, Gaston; Van De Weerdt, Reinhilde; Van Kerkhove, Maria; Wendland
Johansson, G. Leech, S. Conrad & E. Finegan. 1999. Longman grammar of spoken and written English. Harlow, Longman. Rodney Huddleston & Geoffrey Pullum. 2002