Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 35 to 42.
Most desert animals will drink water if confronted with it, but many of them never have any opportunity. All living things must have water, or they will expire. The herbivores find it in desert plants. The carnivores slake their thirst with the flesh and blood of living prey. One of the most remarkable adjustments, however, has been made by the tiny kangaroo rat, who not only lives without drinking but subsists on a diet of dry seeds containing about 5% free water. Like other animals, he has the ability to manufacture water in his body by a metabolic conversion of carbohydrates. But he is notable for the parsimony with which he conserves his small supply by every possible means, expending only minuscule amounts in his excreta and through evaporation from his respiratory tract.
Investigation into how the kangaroo rat can live without drinking water has involved various experiments with these small animals. Could kangaroo rats somehow store water in their bodies and slowly utilize these resources in the long periods when no free water is available from dew or rain? The simplest way to settle this question was to determine the total water content in the animals to see if it decreases as they are kept for long periods on a dry diet. If they slowly use up their water, the body should become increasingly dehydrated, and if they begin with a store of water, this should be evident from an initial high water content. Results of such experiments with kangaroo rats on dry diets for more than 7 weeks showed that the rats maintained their body weight. There was no trend toward a decrease in water content during the long period of water deprivation. When the kangaroo rats were given free access to water, they did not drink water. They did nibble on small pieces of watermelon, but this did not change appreciably the water itent in their bodies, which remained at 66.3 % to 67.2 % during this period.
This is very close to the water content of dry-fed animals (66.5 %), and the availability of free water, therefore, did not lead to any “storage” that could be meaningful as a water reserve. This makes it reasonable to conclude that physiological storage of water is not a factor in the kangaroo rat’s ability to live on dry food.
According to the passage, the results of the experiments with kangaroo rats showed that
A. kangaroo rats store water for use during dry periods
B. kangaroo rats took advantage of free access to water
C. there was no significant change in body weight due to lack of water or accessibility to water
D. a dry diet seems detrimental to the kangaroo rat’s health
Chọn đáp án C
Theo bài đọc, kết quả của các thí nghiệm với chuột túi chỉ ra rằng _________.
A. chuột túi dự trữ nước để sử dụng suốt thời kì khô hạn
B. chuột túi tận dụng việc tự do tiếp cận nguồn nước
C. không có sự thay đổi đáng kể về trọng lượng cơ thể do thiếu nước hay việc tiếp cận đến nguồn nước.
D. một chế độ ăn khô có vẻ có hại cho sức khỏe của chuột túi
Dẫn chứng: Results of such experiments with kangaroo rats on dry diets for more than 7 weeks showed that the rats maintained their body weight. There was no trend toward a decrease in water content during the long period of water deprivation. When the kangaroo rats were given free access to water, they did not drink water. They did nibble on small pieces of watermelon, but this did not change appreciably the water content in their bodies, which remained at 66.3 % to 67.2 % during this period..."(Kết quả của các thí nghiệm với chuột kangaroo trong chế độ ăn khô trong hơn 7 tuần cho thấy rằng những con chuột vẫn duy trì trọng lượng cơ thể của chúng. Không có xu hướng giảm hàm lượng nước trong thời gian dài bị thiếu nước. Khi chúng được cho phép uống nước tự do, chúng đã không uống. Chúng đã ăn vài miếng dưa hấu nhỏ, nhưng điều này không thay đổi đáng kể hàm lượng nước trong cơ thể chúng, mà vẫn ở mức 66,3% đến 67,2% trong thời kỳ này...”)