Read this passage: there is much loose talk of our immunity from immediate and direct invasion from across the seas. obviously, as long as the british navy retains its power, no such danger exists. even if there were no british navy, it is not probable that any enemy would be stupid enough to attack us by landing troops in the united states from across thousands of miles of ocean, until it had acquired strategic bases from which to operate. franklin d. roosevelt, "four freedoms speech: annual message to congress on the state of the union," january 6, 1941 which sentence best states the main idea of this passage from roosevelt's four freedoms speech? a. the united states is being protected by the british navy. b. the united states is not vulnerable to a direct attack. c. the british navy is quickly losing its naval foothold. d. the enemy has acquired bases to launch attacks on the united states.