C. because the enemy would have to cross the heavily guarded sea to get there
Explanation:
In his speech, Winston Churchil, prime minister of Britain during WWII, adresses the british to assure them that they are safe, and that the German army would have it really hard in order to invade british, because they´d find a sea filled up with mines, air bombings and the british army before they could even land a foot on shore and face the british army. They had the sea heavily guarded.
