<span>How you deliver a speech can make all the difference to the audience. TRUE</span>
The answer that you are lookin for is C hope this helps.
The answer would be "to help you decipher symbols and scale."
Without the key, a lot of the symbols would be quite confusing and you wouldn't know if it was 5 miles or 500 miles. Everything else is implied throughout the map, but the key's purpose is definitely to help you decipher symbols and scale.
