Your test is factually wrong on several points.
America isn't a singular continent. There are two continents, North America and South America. Also to say America is not a country is incorrect as well. The United States of America is also correctly called America.
The United States of America has no 51st state. There are 50 states and then some territories. Puerto Rico is a territory, as well as Guam, US Virgin Islands, and a few others.
What is the most spoken language in America would be English. If you mean in the American continents, then you should have phrased it what is the most spoken language in the Americas (plural -- *very important*!). America, singular, is the United States of America.
This whole "test" just screams of trying to conflate terms. America (*singular*) without context is the United States of America. Americas (*plural*) is the correct term to use for the continents. Though you could say either is American.