There is a lot of research showing how difficult it is to change happiness based on external factors.很多研究表明，靠基于外在的因素改变幸福感很难。
There is a lot of research showing how difficult it is to change happiness based on external factors
There is a lot of research showing how difficult it is to change happiness based on external factors.很多研究表明，靠基于外在的因素改变幸福感很难。
