The correct answer to this question would be alternative D) "Roosevelt believed Hitler and Germany were the more dangerous enemy and so had to be defeated first."
The Allied forces focused on Europe first, and dealt with the threat in the Pacific afterwards. The main reason was that two allied capitals (London and Moscow) could be directly threatened by Germany, while Japan could not directly threaten any capitals.
The United Kingdom was the most vulnerable to attacks from Germany, as they had already taken most countries in Western Europe. It was also believed that if Germany was defeated, Italy and Japan would be weakened and might step back. Despite the attack on Pearl Harbor, the United States stuck to the "Europe First" policy.