"Work this one out," said Monica to her colleague. "I drive from my home to the office every morning. At the back of my house is a short, fairly narrow driveway approximately 300 yards long. I drive my car down this driveway in a westerly direction, yet when I stop the car at the end of the driveway it is facing east." "Does the driveway go round in a circle?" asked the colleague.

"No," replied Monica, "it is absolutely straight."

What is the explanation?