A Newspaper Headline Heralds a Finding That an Excess of a Particular

A newspaper headline heralds a finding that an excess of a particular brain chemical is the cause of a certain mental disorder. The article is not convincing to you. What potential flaw do you note in the report?

A) The chemical change could be due to other variables.
B) Chemical changes cannot bring about changes in behavior.
C) The genetic code associated with the chemical has not been identified.
D) Such findings are very difficult to generalize to the entire population.