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stop，food，because，repeat，might，job，rain，connect，color，need，they，come

Have you ever heard of chlorophyll （葉綠素）？The name comes from the Greek words that mean green and leaf （樹(shù)葉）．It's a good name （1）

because

because

chlorophyll gives leaves their green color．
Chlorophyll also has another important （2）

job

job

．It helps plants make food from sunlight，water and air．But leaves must make chlorophyll first，and to do that，they （3）

need

need

light．
During the long days of summer，leaves make lots of chlorophyll，so they can make lots of （4）

food

food

．All that green chlorophyll keeps the leaves looking green．
When fall （5）

comes

comes

，days get shorter．That tells trees to get ready for winter．They begin to store （貯存） food，and they （6）

stop

stop

making chlorophyll．
Without new chlorophyll，leaves quickly lose their green color．Some leaves begin to look yellow or orange．In fact，the yellow and orange （7）

colors

colors

are always in the leaf．They just can't be seen until the green color fades （變淡） and no longer covers （8）

them

them

up．
The leaves on some kinds of trees also start to turn red and purple．Scientists are not sure why，but they think the red color （9）

might

might

protect the leaves from bright sunlight and help the tree store more food before winter comes．That's why you'll see fewer reds in years when fall is （10）

rainy

rainy

or cloudy．The leaves don't need as much protection．