Question 4

Q What is the circulatory system?
A The heart, the lungs and the blood vessels are part of the circulatory system. Humans have about 100,000 kilometers (62,000 miles) of blood vessels in their body. This is enough to circle the
Earth two and a half times! Blood vessels are made up of arteries, veins and capillaries.

Question 3

Q: How many times does the heart beat?
A: The heart beats about 100,000 times in one day. It begins beating from before a child is born and does not stop until the person dies.

Question 2

Q: How big is the universe?
A: No one knows how big the universe really is. There are at least 100 billion galaxies that we know of. However, this number keeps growing as better telescopes are developed and we see more and more galaxies. On top of that, the galaxies are moving away from each other, causing the universe to expand. Some scientists believe that the universe will never stop expanding, while others think that one day it will begin to shrink until it becomes a fireball again.

Question 1

Q: How was the universe formed?
A: The universe was born more than 15 billion years ago. It is believed that the universe began as a small ball of fire. This fireball grew larger and larger until one day it exploded, to form the universe that we know.