It' s never a real problem for us when the weather gets cold． We have many different ways of coping with the cold．We can put on more clothes, stay next to a fireplace, turn on the air conditioner or simply travel to a warmer city to spend the winter．But things are not as easy for plants Unlike humans, plants can’t move to escape the cold or generate heat to keep themselves warm．So how do they manage to survive the freezing winter?
The cold is a big challenge for plants．Their living tissues can be damaged when they freeze．It's like a plant's equivalent(相等物）to frostbite（冻疮）．Also，the process of freezing and thawing（解冻）can cause air bubbles to form in the plant's water transport system．If enough of these air bubbles come together as water thaws they can block the flow of water from the roots to the leaves and kill the plant．
To live through cold weather，plants have developed three strategies，Some plants，such as oak trees, avoid freezing damage by dropping their leaves, before the winter chill sets in-effectively shutting off the flow of water between roots and leaves—and growing new leaves and water transport cells when the warm spring returns. Other plants, pine trees for example, protect them-selves by narrowing their water transport cells, which makes it easier for cells to travel among air bubbles．The third stratef;yi8 also the most extreme．Some plants; die on the ground in winter and start growing as new plants from seeds when conditions get warmer．
However, these smart strategies were developed \nmry8lowly－over millions of years of evolution．This leads scientists to worry that plants may not be able to deal with human-caused climate change, which has only started occurring over the past few decades．Scientists are hoping to find possible ways to save plants from the threat of climate change．
51．What is the text mainly about?
A．Different ways for people to keep warm．
B．How plants live through the freezing winter．
C．How plants develop the 8tratef;ies to keep warm*
D．The ways to save plants from the cold,
52．If the water transport from roots to leaves 18 blocked, ．
A．the plant will suffer from f'rostbite
B．air bubbles will be formed
C．the plant's living tissues will be damaged
D．the plant will be killed
53．Oak trees protect themselves by ．
A．stopping the water transport from roots to leaves
B．dropping their leaves to grow seeds
C．slowing the flow of water from roots to leaves
D．storing enough water in the roots
54．What does the underlined phrase “sets in” mean in Paragraph3?
A．stops B．begins C．leaves D．returns
55．What is the main idea of the last paragraph?
A．Plants can, easily adapt to climate change．
B．Scientists are making efforts to save plants．
C．Climates change is a great threat to plants．
D．Plants are developing new strategies to survive．
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