Final answer:
Sir Gawain suggests that King Arthur sign a month-long treaty with Sir Mordred because he knows they are overmatched and Arthur needs time to confer and plan the battle with his knights.
Step-by-step explanation:
In Le Morte d'Arthur, Sir Gawain suggests that King Arthur sign a month-long treaty with Sir Mordred because he knows that Arthur and his men are overmatched. Sir Gawain is aware that they stand little chance against Sir Mordred's forces and believes that a temporary truce would allow Arthur time to confer and plan the battle with his knights (option D).