Iodine is a well-known example of a trace mineral whose lack in the body creates an easily treated disease. When the thyroid gland is not supplied with sufficient iodine to manufacture hormones, it enlarges and forms a goiter or swelling of the neck. At the same time other symptoms, such as fatigue and sluggishness, weight gain, coldness of the body, and depression, may occur.
In the United States goiter was first noted in the Great Lakes region, where in the 1930s, as many as 40 percent of the people in some areas had goiter, due mainly to iodine-deficient soil. This scarcity had been caused by ice age glaciers melting and washing the iodine out of the soil. The inhabitants of mountainous regions of Europe had suffered from iodine deficiency for centuries for similar reasons. It was discovered in the alpine region of Switzerland in the nineteenth century that in areas in which the drinking water contained less than 0.5 micrograms of iodine per liter there was a high incidence of goiter. In contrast to mountainous or inland regions, areas by oceans or in the vicinity of ocean breezes usually contain enough iodine to prevent this affliction.

单选题 What do goiters generally indicate?
A. A coldness of the body. B. A swelling in the neck.
C. A lack of iodine in the diet. D. A tendency to depression.

单选题 The word "fatigue" in the passage is closest in meaning to ______.
A. exhaustion B. collapse C. numbing D. laziness

单选题 The phrase "rule of thumb" in the passage is closest in meaning to ______.
A. an accurate criterion B. an approximate guide
C. an acceptable quantity D. an important extent

单选题 All the following are mentioned as regions where iodine deficiency occurs EXCEPT ______.
A. mountainous regions
B. regions which were once glaciated
C. areas away from the sea
D. regions which suffer high rainfall

单选题 What is implied about the relationship of the thyroid gland and the kidneys?
A. They help each other to eliminate iodine.
B. They help each other to isolate iodine.
C. The kidneys in some way work against the thyroid gland.
D. The kidneys stimulate the thyroid to produce more iodine.

单选题 The word "here" is the passage refers to ______.
A. thyroid vesicles B. thyroid gland
C. thyroglobulin D. bloodstream

单选题 According to paragraph 4, thyroid hormones ______.
A. affect mainly the neck area
B. control the pituitary gland
C. influence all parts of the body
D. monitor the blood circulation

单选题 Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. The thyroid gland works at keeping its available hormones in the body's cells at consistent levels at all times.
B. The cells of the body need the constant stream of the thyroid gland when faced with declining amounts of iodine.
C. In its attempts to maintain iodine entering the body's cells, the thyroid hormones deplete the amount of available iodine.
D. The iodine in the thyroid remains at the same level in order to maintain the decreasing supply circulating the cells of the body.

单选题 According to paragraph 5, when iodine levels are low ______.
A. the pituitary gland produces less TSH
B. the thyroid gland inhibits hormone production
C. the level of oxygen in the blood increases
D. thyroid vesicles trap more of the iodine from the blood

单选题 The word "induced" in the passage is closest in meaning to ______.
A. treated B. prevented C. handled D. caused

单选题 Look at the four squares, , , and

填空题 Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Research has resulted in a better understanding of how goiters occur.
·______
·______
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A. People living in regions where the soil does not contain enough iodine are more likely to suffer from goiters.
B. Inhabitants of mountainous areas drink water that contains less than 0.5 micrograms of iodine per liter.
C. The thyroid gland is made up of thyroid vesicles, which are balls of cells that contain thyroglobulin, a jellylike substance needed for the manufacturing of thyroid hormones.
D. When the body has a surplus of iodine, the kidneys remove the excess of the mineral from the bloodstream and eliminate it from the body.
E. The increased stimulation of the thyroid causes a swelling in the neck that may become permanent if the thyroid has many periods of low iodine uptake.

F. When supplies of iodine are low in the body the pituitary gland increases the ability of the thyroid gland to trap and increase hormone production.