Which of the following contributed greatly to the fall of the song dynasty?
a. the invention of gunpowder
b. the increase in the chinese population
c. the improvement of the civil service system
d. the vulnerability to invaders from the north

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.

a. competition between france and england for land and power