Correct Answer: D

Rationale: The placenta delivers food and oxygen to the developing organism during pregnancy. It is a temporary organ that forms in the first trimester of pregnancy. Choice A is incorrect as the placenta forms in the first trimester, not the second trimester. Choice B is incorrect as the amniotic sac, not the placenta, encloses the developing organism in amniotic fluid. Choice C is incorrect as the placenta contains blood vessels (arteries and veins) that deliver nutrients to the embryo, not just one large vein.

Correct Answer: A

Rationale: The correct answer is A: Nonnormative. Nonnormative influences are events or experiences that are irregular and unique to the individual, so they do not follow a predictable timetable. These influences can include major life events like winning the lottery or experiencing a natural disaster, and they have a significant impact on a person's development. Choice B, History-graded influences, are events that are common to people of a particular generation due to historical circumstances. Choice C, Age-graded influences, are events that are typical for people of a certain age group. Choice D, Bio-historical, is not a recognized term in developmental psychology.

Correct Answer: B

Rationale: The lifespan perspective on human development assumes that development is multidimensional and multidirectional. This means that development occurs in various domains (such as physical, cognitive, and psychosocial) and can involve gains and losses as individuals age. This perspective recognizes that human development is complex and dynamic, involving various factors and pathways over the course of a person's life. Choices A, C, and D are incorrect because human development is not static and stable (A), can involve both continuous and discontinuous changes (C), and is influenced by a combination of heredity and environment rather than solely by heredity (D).

Correct Answer: A

Rationale: Lev Vygotsky viewed cognitive development as a socially mediated process, emphasizing the role of social interactions and cultural influences in shaping a child's cognitive development. This is in contrast to Jean Piaget, who focused more on individual interactions with the environment. Vygotsky believed that cognitive development is significantly influenced by social interactions with others, highlighting the importance of collaborative learning and cultural context. Choices B, C, and D are incorrect as they do not align with Vygotsky's perspective on cognitive development.

Correct Answer: B

Rationale: Low-level radiation, whether from industrial leakage or medical X-rays, can increase the risk of childhood cancer by potentially damaging the developing fetus's cells. Even though the risk is relatively low, it is still a significant concern that should be acknowledged and monitored closely, especially during prenatal development. Choice A is incorrect as low-level radiation can still be harmful on its own without the need to be combined with other teratogens. Choice C is incorrect because low-level radiation exposure can indeed cause lasting damage, especially in the context of childhood cancer risk. Choice D is incorrect because low-level radiation exposure, even during the last trimester, can pose risks to the developing fetus and is not considered entirely safe.