Political economics Senior High over 5 yearsago

答えは2なのですが、このinはどこから来たのでしょうか？

/〆 82介入 (2) The seience of medienel ( ) progress has been Very rapid Jateh り1S perhaps the most important of al sciences. の ① for as ② which ③ sincee ④ so (関西学院