Final answer:
The key theme of phrenology by Franz Joseph Gall is that the size and shape of the brain, as indicated by the skull, can reveal personality traits and tendencies, including criminal behavior. The correct answer to the question is option B.
Step-by-step explanation:
The key theme of phrenology, as proposed by Franz Joseph Gall, is that the brain size and shape are indicative of personality traits, character, and mental abilities. According to phrenology, these physical characteristics of the skull could be measured to reveal the sizes of the brain areas underneath. This was believed to provide information that could be used to determine a person's proclivities, including whether a person was friendly, murderous, good with languages, and so on.
Answering the multiple-choice question, the correct option is B) Brain size and shape are indicative of criminal tendencies. This directly relates to Gall's belief that different parts of the brain, as evidenced by various bumps and shapes on the skull, were responsible for different human traits and tendencies, including criminal behavior.