The Short Answer:
High and low tides are caused by the moon. The moon's gravitational pull generates something called the tidal force. The tidal force causes Earth—and its water—to bulge out on the side closest to the moon and the side farthest from the moon. These bulges of water are high tides.
Can you take a better picture so that all of the words can be seen,maybe horizontally?
Answer:
The reasons that cities boomed during the Middle Ages are more employment opportunities, increased trade, and growing interest in culture and art.
