1. Algeo, J. (2006). British or american english? A handbook of word and grammar patterns. UK: Cambridge University Press.
2. Cambridge Advanced Learners’ Dictionary (2008). Cambridge University Press.
3. Colins Cobuild Advanced Learners’ English Dictionary (2006). Harper Colins.
4. Farrell, T. & Martin, S. (2009). To teach standard english or world englishes: A balanced approach to instruction. Teaching Forum, 2, 2-7.
5. Finnie, R., Frain, C., Hill, D. H., & Thomas, K. (2010). Top grammar: From basic to upper intermediate. Helbling Languages.