Answer:
D: Religious persecution motivated Brigham Young and his Mormon followers to cross the plains and establish a community in the west.
Explanation:
In 1844, Mormon's founder and prophet 'Joseph Smith' was murdered. Since then, they were continuously facing mob violence in Illinois, place where they were settling initially. Then, these Mormons extended their support to Brigham Young who was a new leader.
Brigham Young and his members (Church of Jesus Christ) moved to Utah's 'Great Salt Lake' Valley and settled there. They had moved to avoid religious discrimination. Today, their population is around 2 million in Utah.