People have always wondered about these pictures inside their heads. But dreams come only

with sleep. It has been hard to find out more about them. People have tried to make their dreams work for them. Some people have thought dreams were a way into the past. Others have seen dreams as a path to follow. Some have even thought dreams could help the sick.

Dreams start when the" inner mind" is opened. This is the place where memories are stored. Often dreams are hard to understand. This is because the inner mind sometimes uses symbols.

Symbols are words or pictures that stand for something else. Most symbols stand for things that have just happened. They can also stand for thing that happened a long time ago. By using symbols, the inner mind can show people things in dream5 that they did not know about themselves. The symbol is another way of showing what really happened.

Dreams have close ties with sleep. People sleep 33 percent of their lives. This is called sleep time. People dream during 25 percent of sleep time.

While they are sleeping, people "tune out" the things around them. But when they dream, people may seem to sense the same things they de when they are awake. They may sometimes see, hear, taste, smell, and feel things in their dreams. These things often seem as real to people when they are asleep as when they are awake.

Even though sleeping people seem to be resting, their bodies are working. Scientists have found that the eyes of sleeping people are moving. They have also found out that their brains are sending out waves.

Why has it been difficult for people to find out more about dreams？

A．Different people have different ideas about dreams.

B．Different dreams have different meanings.

C．People can only have their dreams studied when they are sleeping.

D．People only have dreams when they are sick.