Several types of evidence have linked bipolar disorder to genes. Which one of the following is NOT ...

Several types of evidence have linked bipolar disorder to genes. Which one of the following is NOT
  one of these types of evidence?
  A. Biochemical studies
  B. Twin studies
  C. Adoption studies
  D. Association studies
  E. Studies involving degrees of relatedness

Question 2

The mutant huntingtin protein that results in Huntington disease
  A. causes a decrease in production of another protein.
  B. leads to degeneration of cells in the brain's striatum.
  C. is toxic to brain cells.
  D. leads to degeneration of cells in the brain's striatum and is toxic to brain cells only.
  E. has all of these traits.