There is established a Department of Homeland Security, as an executive department of the United States. . . . The primary mission of the Department is to (a) prevent terrorist attacks within the United States; . . .(c) minimize the damage, and assist in the recovery, from terrorist attacks that do occur within the United States; (d) carry out all functions of entities [separate things] transferred to the Department. . . . According to this legislation, what is the main function of this department