Questions 11 - 13 are based on the following talk about finding books. You now have 15 seconds to read Questions 11 - 13. What is the topic of the man’s research paper

A．The data 'about the 97% population is rich.
B．Historians had a set of numbers indicating the date of their birth, marriage and death.
C．The 97% population had nothing that is worth of recording.
D．The data historians had presented a vivid picture of the 97% population.

A．They had new findings.
B．They expanded the period defined as pre-industrial Europe.
C．They investigated the common people who took up the majority of the population.
D．The investigations were on the kings, generals ,judges, nobles, bishops, and local magnates.