The reason
去国外学习 » Study abroad 究其原因 » The reason for 不吃三餐,用点心(snack)代替(replace..
Among the reasons for
他们的效率很高 » Their efficiency is very high 究其原因 » Among the reasons for 和朋友在一起我们会感到开心。我从来不和朋友打架。