Which of the following is the best description of an obelisk?
a massive sundial that helped Egyptians calculate the precise time of day using the shadows of the sun
a massive sculpture of a man with the head of a lion made of natural soft limestone
a tall, four-sided tower covered with engravings and tapering toward a point at the top
a large stone monolith of a Pharaoh's head, flanked by a rearing cobra