Atmospheric pressure can support a

Áp suất khí quyển có thể hỗ trợ một cột nước lên đến 10 mét, cao. Nhưng nhà máy có thể di chuyển nước cao hơn nhiều, cây sequoia có thể bơm nước để đầu rất của nó, nhiều hơn 100 mét so với mặt đất. Cho đến cuối thế kỷ 19, sự chuyển động của nước trong cây và thực vật talls khác là một bí ẩn. Một số nhà thực vật học đưa ra giả thuyết rằng các tế bào sống vật hành động như máy bơm, nhưng nhiều thí nghiệm đã chứng minh rằng thân cây của nhà máy trong đó tất cả các tế bào bị giết vẫn còn có thể di chuyển nước lên tầm cao đáng. Lời giải thích khác cho sự chuyển động của nước trong các nhà máy đã được dựa trên áp lực gốc, một đẩy trên mặt nước từ gốc rễ ở dưới cùng của nhà máy. Nhưng áp lực gốc là tuyệt vời không phải là gần đủ để đẩy nước để các ngọn cây cao, Furthermore, các loài cây lá kim, đó là một trong những cây cao nhất có bất thường thấp gốc áp lực._____If water is not pumped to the top of a tall tree, and if it is not pushed, to the top of a tall tree, then we may ask. How does it get there? According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves, a negative pressure or tension is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion ( the attraction between water molecules) are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken.1. How many theories does the author mention?(A) One(B) Two(C) Three(D) Four2. The passage answers which of the following questions ?(A) What is the effect of atmospheric pressure on foliage?(B) When do dead cells harm plant growth?(C) How does water get to the tops of trees?(D) Why is root pressure weak?3. The word "demonstrated" in line 6 is closest in meaning to(A) ignored
(B) showed
(C) disguised
(D) distinguished

4. What do the experiments mentioned in lines 6-8 prove?
(A) Plant stems die when deprived of water.
(B) Cells in plant sterns do not pump water.
(C) Plants cannot move water to high altitudes.
(D) Plant cells regulate pressure within stems.

5. How do botanists know that root pressure is not the only force that moves water in plants?
(A) Some very tall trees have weak root pressure.
(B) Root pressures decrease in winter.
(C) Plants can live after their roots die.
(D) Water in a plant's roots is not connected to water in its stem.

6. Which of the following statements does the passage support?
(A) Water is pushed to the tops of trees.
(B) Botanists have proven that living cells act as pumps.
(C) Atmospheric pressure draws water to the tops of tall trees.
(D) Botanists have changed their theories of how water moves in plants.

7. The word "it" in line 13 refers to
(A) top
(B) tree
(C) water
(D) cohesion-tension theory

8. The word "there" in line 15 refers to
(A) treetops
(B) roots
(C) water columns
(D) tubes

9. What causes the tension that draws water up a plant?
(A) Humidity
(B) Plant growth
(C) Root pressure
(D) Evaporation

10. The word "extend" in line 19 is closest in meaning to
(A) stretch
(B) branch
(C) increase
(D) rotate

11. According to the passage, why does water travel through plants in unbroken columns?
(A) Root pressure moves the water very rapidly.
(B) The attraction between water molecules is strong.
(C) The living cell of plants push the water molecules together.
(D) Atmospheric pressure supports the columns.

12. Why does the author mention steel wire in line 24?
(A) To illustrate another means of pulling water
(B) To demonstrate why wood is a good building material
(C) To indicate the size of a column of winter
(D) To emphasize the strength of cohesive forces in water