Since 1975 there has been in the United States a dra- matic decline i

When everyone was getting Measles, no one had Peterson's disease; Now the incidence of Measles has fallen, Peterson's back. It proves only one thing, there's some linkage between Measles & Peterson's OR something far outrageous such as outbreak of a new virus that causes Peterson's disease or something.
Well, in the given options,

(A) Hereditary factors determine in part the degree to which a person is susceptible to the virus that causes Peterson's disease. (then what changed in hereditary that it almost come up suddenly after Measles declined)
(B) The decrease in traditional childhood diseases and the accompanying increase in Peterson's disease have not been found in any other country. (irrelevant, doesnt prove the reason for increase)
(C) Children who contract measles develop an immunity to the virus that causes Peterson's disease. (This sets the story up for the linkage between Measles and Peterson's disease)
(D) Persons who did not contract measles in childhood might contract measles in adulthood, in which case the consequences of the disease would generally be more severe. (the facts of the case differ here)
(E) Those who have contracted Peterson's disease are at increased risk of contracting chicken pox. (Out of scope).

Option C is the answer

(A) Hereditary factors determine in part the degree to which a person is susceptible to the virus that causes Peterson's disease.

Option (A) discusses hereditary factors that affect susceptibility to Peterson's disease. While this may be relevant to understanding why some individuals are more susceptible than others, it doesn't directly explain the increased incidence of Peterson's disease among children in the context of the decline in traditional childhood diseases. It's more about individual susceptibility, not the overall trend.

(B) The decrease in traditional childhood diseases and the accompanying increase in Peterson's disease have not been found in any other country.

Option (B) points out that this specific trend of decreasing traditional childhood diseases and increasing Peterson's disease hasn't been observed in other countries. While this information is interesting, it doesn't explain why this trend is happening in the United States, which is what we're trying to understand.

(C) Children who contract measles develop an immunity to the virus that causes Peterson's disease.

Option (C) is the correct answer because it directly addresses the issue. It explains that children who contract measles develop immunity to the virus causing Peterson's disease. The decrease in measles cases due to vaccination programs means fewer children are contracting measles and, as a result, not developing immunity to Peterson's disease. This lack of immunity could lead to an increased incidence of Peterson's disease among children.

(D) Persons who did not contract measles in childhood might contract measles in adulthood, in which case the consequences of the disease would generally be more severe.

Option (D) discusses the consequences of contracting measles in adulthood, but it doesn't directly explain the increased incidence of Peterson's disease among children. It's more focused on the potential consequences of measles in adulthood, which is a different issue.

(E) Those who have contracted Peterson's disease are at increased risk of contracting chicken pox.

Option (E) discusses the increased risk of contracting chickenpox for those who have Peterson's disease, but it doesn't address why there is an increased incidence of Peterson's disease among children in the first place. It's more about the consequences of having Peterson's disease.