The U. S. government imprisoned certain people after the attack on Pearl Harbor because

A. the immigrant population in the U. S. had reached a level unacceptable to most people.

B. the U. S. government was concerned about people being in sympathy with the enemy.

C. the U. S. government wanted to isolate themselves from the rest of the world.

D. the immigrant population in the U. S. engaged in mass anti-government demonstrations.