Which ruler unified China under the Tang Dynasty?

Which of the following was a factor that attracted settlers from the east to the oregon country in the 1840s? a.) the absence of native americans in the oregon country attracted many eastern settlers to the region. b.) the discovery of gold in 1848 caused a huge migration of people into the oregon country. c.) the oregon country’s status as an area of religious freedom attracted many mormons from the east. d.) married couples could claim 640 acres of free land in the oregon country.