Correct Answer: A

Rationale: The correct answer is A. Studying specific gene defects is not a common method for investigating genetic influences. Choices B, C, and D are common methods used in genetic research. Twin studies help determine the heritability of traits, adoption studies compare similarities between adopted individuals and their adoptive families versus biological families, and family history studies track the inheritance patterns of traits within families.

Correct Answer: C

Rationale: The correct answer is C: 'Interaction between genetics and environment.' The genetic study of identical twins reared apart helps in understanding how both genetics and environment play a role in shaping an individual's traits and behaviors. This type of study allows researchers to tease apart the effects of genetic inheritance from those of environmental influences. Choices A, B, and D are incorrect because the study of identical twins reared apart specifically focuses on the interplay between genetics and environment, rather than solely on differences in brain function, genetic influence on behavior, or the role of environmental factors alone.

Correct Answer: C

Rationale: The correct answer is C: 'Undercontrolled behavior; overcontrolled behavior.' The question highlights a cultural difference in behavior tendencies between American and Thai children. American children are usually characterized by undercontrolled behavior, while Thai children tend to exhibit overcontrolled behavior. Choice A (Aggressive behavior; calm behavior) is incorrect as the question does not mention aggressive or calm behavior as the contrasting traits between the two groups. Choice B (Overcontrolled behavior; undercontrolled behavior) is incorrect because the described behavior patterns are reversed based on the question's context. Choice D (Equal behavioral traits in both cultures) is incorrect as the question explicitly states differing behavior patterns in American and Thai children.

Correct Answer: B

Rationale: Culture is essential in shaping our perceptions and definitions of abnormal behavior. Choice A is incorrect because culture actually plays a significant role in understanding abnormal behavior. Choice C is incorrect as culture can have a considerable impact on how abnormal behavior is expressed. Choice D is incorrect because culture influences not only the treatment but also the understanding of abnormal behavior.

Correct Answer: A

Rationale: In understanding abnormal behavior, it is crucial to differentiate between necessary, sufficient, and contributory causes. Necessary causes are those that are required for a disorder to develop, meaning that without them, the disorder would not occur. However, their presence does not guarantee the occurrence of the disorder. Sufficient causes, on the other hand, are those that alone can guarantee the development of a disorder, but they are not the only factors that can lead to it. Contributory causes are factors that increase the likelihood of a disorder but are not essential on their own nor do they guarantee the disorder. Therefore, choice A is the correct answer as it accurately describes the role of necessary causes in the development of abnormal behavior. Choices B, C, and D are incorrect as they misrepresent the definitions and roles of sufficient and contributory causes in causing abnormal behavior.