阅读理解

　　When you look at clouds, you will notice that there are many different kinds．Some clouds are high and thin, some are white and fluffy(蓬松的)and others look dark and heavy．

　　There are four kinds of clouds, They are high clouds, middle clouds, low clouds, and clouds that grow vertically(垂直的)．And that clouds in these four groups are name for the way they look．

　　Cirrus clouds are high clouds that are more than 5kilometers above earth．Cirrus clouds look like curly hair, and the word cirrus just means "curl of hair"．Some high clouds that look like layers(层)are called cirrostratus clouds．The word stratus means "layer"．

　　About 3 to 6．5 kilometers above earth are the middle clouds．Altostratus clouds are light gray, and Altocumulus clouds are very fluffy．Another cloud that sometimes can be a middle clouds is Nimbostratus cloud．Nimbo comes from the word nimbus, which means "heavy rain"．These clouds make a gray layer from which rain and snow falls．

　　The low clouds are no higher than about 1．6 kilometers above earth．Two kinds of clouds are often found here．Stratocumulus clouds are light and dark．Stratus clouds are very low．

　　The fourth group of clouds grows vertically．These clouds have a base near the ground but rise to a great height．Cumulus clouds can grow up on top of one another．When they grow up high, they are called cumulonimbus clouds．These clouds can rise as high as 18 kilometers．