It is a must be true question. So the correct answer must a paraphrase of a statement or a combinations of statements in the stem.

(A) At least some people observed during the study had an increase in blood calcium levels during the ten-year period. =>the study is about the test of patients's blood, but is does not specifically state the calcium decreases or increases. So the answer is not correct.

(B) People with the hereditary disorder are at no greater risk of developing laryngeal polyps than are people with low blood calcium levels who do not have the disorder. => the only relationship between hereditary disorder and low blood calcium levels stated in the stem is the cause-result relationship. There is no comparison of the risks of developing laryngeal polyps among them.

(C) The amount by which the researchers overestimated the likelihood of developing polyps decreased after the first five years of the study. => the stem only says the researchers overestimates the likelihood of developing polyps within the next five years, not the amount of patients who are diagnosed.

(D) The percent of patients in the study with laryngeal polyps consistently increased over the ten-year period. =. Not stated.

(E) Prior to the end of the study, the researchers had reason to believe that at least some of their predictions had been overestimates. => It is the paraphrase of the last sentence. CORRECT answer.