The correct choice is Option 2: 'Although they were nervous at first, as they worked together, conversations started and it became fun.' The second paragraph states: '最初は、知らない人ばかりで少し緊張しましたが、一緒にごみを拾っているうちに...簡単な会話が始まり、だんだん楽しくなってきました' (At first, I was a bit nervous with only strangers, but while we were picking up trash together, simple conversations started and it gradually became fun). This matches Option 2 perfectly. Option 3 is wrong because there is no mention of rain. Option 4 is wrong because the author says 'これからも毎月参加しようと思っています' (I plan to participate every month from now on), implying it's a monthly event.