1. Albrecht, S., Cullen, C., Davies, K., Dunlop, M., Elliott, M. & Stevenson, L. (2018). Cambridge Assessment English. Cambridge University Press. https://www.cambridgeenglish.org/Images/461823-young-learners-revision-publication.pdf
2. Amazon Web Services (AWS). (2016). Amazon Polly [Text-to-Speech Service]. www.aws.amazon.com/polly/