Leaves are nature’s food factories. Plants take water from the ground through their roots. They take a gas called carbon dioxide (CO2) from the air. Plants use sunlight to turn water and CO2 into glucose（葡萄糖）.Glucose is a kind of sugar. Plants use glucose as food for energy to grow. The way plants turn water and CO2 into glucose is called photosynthesis (光合作用).That means “putting together with light .” A chemical called chlorophyll helps make photosynthesis happen. Chlorophyll is green. It gives plants their green colour. As summer ends and autumn comes, the days get shorter and shorter. This is how the trees “know” to begin getting ready for winter.

During winter, there is not enough light or water for photosynthesis .The trees will rest, and live on the food they have stored during the summer. They begin to close their food-making  factories. The green Chlorophyll disappears from the leaves. Then, we begin to see yellow and orange colours. A few of these colors stay in the leaves all the time. We just can’t see them in the summer, because they are covered up by the green Chlorophyll.

Red and purple colors we see in leaves are made mostly in the autumn. In some trees, like maples, glucose is stored in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into red. The brown color of trees like oaks is made from wastes left in the leaves.

52 the underlined word“chlorophyll” in the first Para means_________in Chinese.

A 叶绿素           B 氧气          C 胡萝卜素      D 蛋白质

53 The way _________is called photosynthesis.

A  Plants get CO2 from the air           B  plants take water from the ground

C  plants turn water and CO2 into glucose.  D Plants use glucose as food for energy to grow.

54 The gas called carbon dioxide is from the_________

A  ground      B roots        C air      D sunlight

55 Which of the following is not true?

A．when autumn and winter come, the days get shorter and shorter.

B．During winter trees rest and live on the food they store during the summer.’

C．During winter small amounts of yellow and orange colors are kept in the leaves all the time.

D．Trees begin to stop making food in summer.