Theory
https://www.slideshare.net/FaizSilalahi/formal-vs-informal-language-232535753
https://www.londonschool.com/blog/10-differences-between-formal-and-informal-language/
https://www.eslbuzz.com/the-difference-between-formal-and-informal-language/
https://languagetool.org/insights/post/formal-vs-informal-style/
Practice
https://wordwall.net/en-gb/community/formal-and-informal-language
https://www.flo-joe.co.uk/cae/students/writing/register/index.htm
https://www.proprofs.com/quiz-school/story.php?title=formal-vs-informal-language
https://www.liveworksheets.com/w/en/english-second-language-esl/78395
MAILS
Practice
http://learnenglishteens.britishcouncil.org/skills/writing-skills-practice/email-about-sports
http://learnenglishteens.britishcouncil.org/skills/writing-skills-practice/invitation
http://learnenglishteens.britishcouncil.org/skills/writing-skills-practice/travelling-abroad
CONNECTORS OF ADDITION
https://www.liveworksheets.com/w/en/english-second-language-esl/805876
https://www.liveworksheets.com/w/en/english-second-language-esl/748474
https://www.englishexercises.org/makeagame/viewgame.asp?id=1792
https://wordwall.net/es-ar/community/connectors-of-addition
CONNECTORS OF CONTRAST
https://www.liveworksheets.com/w/en/english-second-language-esl/1509909
https://www.liveworksheets.com/w/en/english-second-language-esl/1141342
https://www.usingenglish.com/quizzes/89.html
https://www.usingenglish.com/quizzes/220.html
https://www.eltbase.com/quiz/148_01.htm
https://www.educaplay.com/learning-resources/6511043-connectors_of_contrast.html
RREPORTS
Theory
https://engxam.com/handbook/how-to-write-a-report-b2-first-fce/
https://www.languages247.com/writing-in-english/writing-a-report/
Practice
https://learnenglishteens.britishcouncil.org/skills/writing/b2-writing/report
https://www.liveworksheets.com/es/w/en/english-second-language-esl/2209686