18．Sleep and dreams have interested people for centuries．Scientists are learning more about sleep，but they still know very little about why we dream．
（36）D First，we have most of our dreams during REM （rapid eye movement） sleep．At this time，the brain is very active．Second，everyone dreams，even if we can't remember doing so when we awake．（37）FWhile we are asleep，it works more slowly and sometimes puts our thoughts and memories together in strange ways．
（38）BSome believe that our dreams are relevant to thoughts and feelings that we experience while we are awake．Many dreams researchers think that a dream about death，for example，is really about an important life change．（39）G A dream about teeth---especially broken or loose ones---may suggest stress or fear．Dreams in which you are flying often represent freedom or escape．
Researchers think people in our dreams can tell us something about ourselves．If the person in the dream was yelling，for example，maybe you are angry．（40）C
There is still a lot about dreaming that we do not understand．By learning more about our dreams，we may learn more about ourselves．
A．Dreams may be more important than sleep．
B．Scientists do not know for certain why we dream．
C．If he or she was scared then maybe you are terrified of something．
D．Modern research can tell us some important things about dreams．
E．There are three things you should pay attention to to have a sweet dream．
F．Finally，a part of our brain helps us to understand daily experience we have．
G．Dreams about telephones are thought to be about giving or receiving messages．
