In the text, you read this about immigration: The period from the 1990s to the 2000s saw the largest numbers of immigrants in the country’s history. During that time, almost one million immigrants arrived in America each year from all over the globe, representing a wide variety of cultures and religions. Today, immigrants account for more than 10 percent of the total American population." What was the main cause of the flux of immigration that occurred in the 1990s to 2000s in the United States?

a. The falling birthrate led to quotas being raised.

b. Strict immigration laws were somewhat relaxed.

c. Immigrants were encouraged with offers of free land.

d. New industries opened up that required talent from around the world.