The correct statement is:
A) A dichotomous key uses question parts to identify organisms.
A dichotomous key typically presents a series of choices that lead the user through a series of questions about the observable traits of organisms until the desired organism is identified. While options B and C mention photographs, they are not inherent to the nature of a dichotomous key, which relies on decision-making through questions. Option D is partly true, as a dichotomous key does utilize observable traits, but it is not entirely accurate as it emphasizes samples rather than the question format of the key.