어법상 판단 문제 급한 질문이요~!

after moving to a new city, i ①joined the company baseball team. being the oldest player, i had to play the outfield. during one game, i made a ②few mistakes. then i kept ③hearing someone shouting, “way to go, mr. green” and “you can do it, mr. green.” i was amazed someone would know my name in this strange city. after the game, i met my wife and son and asked ④that they knew who was shouting encouragement in the stand. my son spoke up and said, “dad, it was me.” i asked why he was calling me mr. green and he replied, “i didn’t want anyone ⑤to know that i’m your son.”

2010 고1 기출인데 답이 4번으로 되있어요~
근데 왜 4번인지...설명 좀 부탁드리겠습니다!