Nearly all adults in the community of Amaretti, including pregnant women, engage in ritual fasting throughout December and January. A recently completed study has revealed that, on the annual cognitive tests given to Amaretti's first-graders in each of last ten years, nearly 25% of the students scoring in the top fifth of the class, but only about 2% of those scoring in the bottom fifth, were born in November. Because pregnancy lasts nine months, only the mothers of children born in November would not have fasted during the entire pregnancy; therefore, the ritual fasting must have detrimental effects on developing babies.

Which of the following, if true, most weakens the argument?

A. No comparable data are available for students who were in first grade in Amaretti more than 10 years ago.

B. First-grade students who are absent from school when the cognitive tests are administered do not have the opportunity to take them at a later time.

C. Each school grade in Amaretti is composed of students born between November 1 of a certain year and October 31 of the following year.

D. In Amaretti, non-cognitive birth defects, such as physical deformities, occur at a much lower rate among babies born in November than among babies born in other months

E. In a typical year in Amaretti, between one-fourth and one-fifth of all babies, are born in November.