In the early days of sea travel, seamen on long voyages lived exclusively on salted meat and biscuits. Many of them died of scurvy (坏血病), a disease of the blood which causes swollen gums, livid white spots on the flesh and general exhaustion. On one occasion, in 1535, an English ship arrived in Newfoundland with its crew desperately ill. The men´s lives were saved by Iroquois Indians who gave them vegetable leaves to eat. Gradually it came to be realized that scurvy was caused by some lack in the sailors´ diet and Captain Cook, on his long voyages of discovery to Australia and New Zealand, established the fact that scurvy could be warded off by the provision of fresh fruit for the sailors.
Nowadays it is understood that a diet which contains nothing harmful may yet result in serious disease if certain important elements are missing. These elements are called “vitamins”. Quite a number of such substances are known and they are given letters to identify them, A, B, C, D, and so on. Different diseases are associated with deficiencies of particular vitamins. Even a slight lack of Vitamin C, for example, the vitamin most plentiful in fresh fruit and vegetables, is thought to increase significantly our susceptibility (敏感度) to colds and influenza.
The vitamins necessary for a healthy body are normally supplied by a good mixed diet, including a variety of fruit and green vegetables. It is only when people try to live on a very restricted diet, say during extended periods of religious fasting (斋戒), or when trying to lose weight, that it is necessary to make special provision to supply the missing vitamins.
51. Scurvy is a disease that is provoked by ____
A. salted meat and biscuits              B. exhaustion
C. want of some essential substances      D. lack of fresh vegetables and fruits
52. In the last sentence of Paragraph 1, “warded off” could probably be replaced by____.
A. got rid of     B. killed     C. avoided     D. cleared away
53. To avoid such disease as scurvy, it´s better for us ____.
A. not to eat much salted meat
B. to supplement our diet with various vitamin pills
C. to have more fresh fruit and vegetables
D. to develop a good dietary habit
54. Based on the passage we can safely conclude that if our diet is not comprehensive enough ____.
A. vitamin pills are of no avail
B. nutritious food might be unhealthy
C. vegetable leaves can be a good remedy
D. religious fasting may help out a lot
55. Which of the following sentences best expresses the central ideal of the passage?
A. Deficiencies of Vitamin C may cause serious diseases.
B. Fresh fruit and green vegetables contain enough nutrition that is necessary for a healthy body.
C. Vitamins play a vitally important role in people´s health.
D. A good mixed diet normally supplies sufficient vitamins for us.

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