https://www.english-grammar.at/online_exercises/connectives/con004-linking-words.htm

https://www.english-grammar.at/online_exercises/connectives/con013.htm

https://www.english-grammar.at/online_exercises/connectives/con014.htm

https://www.english-grammar.at/online_exercises/connectives/con015.htm

https://www.english-grammar.at/online_exercises/connectives/con016.htm

https://www.ecenglish.com/learnenglish/lessons/subordinating-conjunctions/