SAT English Practice Question

In the 1800s, the United States was a land of great exploration and expansion. The Louisiana Purchase doubled the size of the country, while the discovery of gold in California spurred a massive westward migration. These events led to the development of new technologies and industries, and the United States quickly became a global power. However, the rapid expansion of the country also had its downsides. The growth of cities led to overcrowding and poverty, and the exploitation of Native Americans during westward expansion was a dark chapter in US history. What is the best way to combine these two sentences without changing the meaning: "The growth of cities led to overcrowding and poverty. The exploitation of Native Americans during westward expansion was a dark chapter in US history."?

1. A.The growth of cities led to overcrowding and poverty; the exploitation of Native Americans during westward expansion was a dark chapter in US history.
2. B.The growth of cities led to overcrowding and poverty, but the exploitation of Native Americans during westward expansion was a dark chapter in US history.
3. C.The growth of cities led to overcrowding and poverty, as did the exploitation of Native Americans during westward expansion, which was a dark chapter in US history.
4. D.The growth of cities led to overcrowding and poverty; as did the exploitation of Native Americans during westward expansion, which was a dark chapter in US history.