CONNECTS two or more than two words, phrases, clauses, sentences, etc.'When' is a conjunction that is used to denote 'at or during the time that'.For eg.- I loved maths when I was at school.In the given sentence, during the time that the TEAMS were being introduced, people were clapping and cheering.Hence, option 4 is the correct answer.Let's look at the remaining options.WordUsageExample Sentenceif(introducing a conditional clause) on the condition or supposition that; in the event that.If you have a complaint, write to the director.so thatused before the clause which indicates the purposeWe left a message with her secretary so that she would know we have come.in caseas a provision against SOMETHING happening or being true.We PUT on thick jumpers, in CASE it was cold