The education system of the song dynasty, allowed people from low social classes to have quality education and to obtain valued and well-paid professions.
Explanation:
The song dynasty education system allowed people to have full access to education and participate in examinations to become public officials, regardless of which social class the person belonged to.
This allowed people from lower social classes to rise their position through their professions, moving up the class and reaching higher levels within society, that is, education promoted social mobility.
I would choose answer 2, since that answer is based on a same size consisting of more than 1 person, making it applicable to statistic analysis and have an input in the observational study. The other questions ask for one data point, which isn't statistical
