PART of it.of: You use of after the name of someone or something to introduce the institution or PLACE they belong to or are connected with.so: You use so to refer back to something that has just been mentioned.for: If something is for someone, they are intended to have it or benefit from it.The correct preposition here is ‘into’ as we move ‘into’ something. The usage of the other prepositions does not FIT here. THUS option 3 is the correct answer.