Siblings tend to have similar personalities; if environment outweighs heredity in personality development, siblings raised together should presumably have more similar personalities than those raised apart. A recent study of siblings in both situations measured 11 key traits through a questionnaire, and concluded that 7 of the 11 are primarily products of heredity.
Which of the following, if established, would cast the most double on the study results?
(A) Fewer than half of the pairs of siblings studied were raised separately.
(B) The siblings were studied were all within a 10- year age range.
(C) Some of the traits that the study attributed to heredity developed in the separately raised siblings because those pairs all grew up in similar families.
(D) Although over half the traits measured were determined to be linked to heredity, the nature of those traits varied widely.
(E) The 11 traits that were measured constitute a representative sample of a larger, generally accepted pool of key personality traits.
Ans is C
pls optional considerations of the correctness of the answer?