Correct Answer: B

Rationale: In the last weeks of pregnancy, most fetuses assume an upside-down position known as the head-down position or vertex presentation. This position is ideal for a smoother labor and delivery process as it helps the baby move through the birth canal. Fetal growth has already slowed down at this stage, so option C is incorrect. Option A is inaccurate as the fetus typically gains weight in the final weeks. Option D is incorrect because the fetus relies on the mother's immune system while in the womb.

Correct Answer: B

Rationale: Arnold Gesell is generally regarded as the founder of the child study movement, emphasizing the importance of observing and documenting children's behaviors to understand their development. While he was a significant figure in child development research, he did not specifically write child-rearing books for parents, foreshadow lifespan research, or construct the first successful intelligence test. Choice A is incorrect as Gesell's focus was more on research rather than writing child-rearing books. Choice C is incorrect as Gesell's main contributions were in child development, not specifically in aging research. Choice D is incorrect as Gesell is not credited with constructing the first successful intelligence test.

Correct Answer: C

Rationale: Three-month-old Jefferson will likely listen longer to human speech compared to nonspeech sounds because infants have a natural preference for speech sounds. This preference is believed to be attributed to their biological readiness to learn language and communicate with others. Choice A is incorrect because voices are a form of human speech, which is preferred over pure tones. Choice B is incorrect as noises do not necessarily engage infants' attention as effectively as human speech. Choice D is incorrect because Jefferson is more likely to listen longer to his native language rather than a foreign language at this early age.

Correct Answer: D

Rationale: In this scenario, the researchers randomly assigned adolescents to either a single-grade classroom or a mixed-age classroom, which is an example of a field experiment. A field experiment involves manipulating independent variables in a natural setting to observe the effects on participants. This design allows for more control over variables compared to naturalistic observation, case studies, or natural experiments. Naturalistic observation involves observing subjects in their natural environment without manipulating any variables. A case study focuses on in-depth analysis of a single individual or a small group. A natural experiment involves observing naturally occurring events without intervention or manipulation by the researcher.

Correct Answer: B

Rationale: Babies who spend more time alert are likely to have a slight advantage in mental development. Being alert allows babies to engage with their surroundings, explore, and learn, which can contribute to their cognitive development. This is different from social development, which is more related to interactions with others, and not necessarily impacted by the amount of alertness a baby displays. Choices A, C, and D are incorrect because there is no direct correlation between a baby's alertness and their parents' feelings of incompetence, a big disadvantage in social development, or the effort parents need to soothe them.