参考資料  http://www.write-better-english.com/writing-style.aspx  http://ezinearticles.com/?The-Difference-Between-Formal-and-Informal-Writing&id=594208  http://linguapress.com/grammar/styles-of-english.htm  http://www.wikihow.com/Avoid-Colloquial-(Informal)-Writing  http://forum.wordreference.com/threads/formal-way-of-saying-to-carry-out-an-activity.2482262/  http://dictionary.cambridge.org/us/grammar/british-grammar/formal-and-informal-language  http://www.englisch-hilfen.de/en/words/informal1.htm  https://guinlist.wordpress.com/2015/06/29/108-formal-and-informal-words/  http://www.engvid.com/english-resource/formal-informal-english/  http://ielts-academic.com/2012/07/06/informal-formal-vocabulary-for-ielts/  http://pespmc1.vub.ac.be/papers/formality.html