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.

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: Unlike adults, newborn babies see nearby objects most clearly. This is due to the fact that newborns have a limited ability to focus their eyes on objects that are farther away. Their visual acuity is not fully developed at birth, leading to clearer vision of objects situated at a close distance. Choice A is incorrect because newborn babies have a well-developed sense of smell. Choice C is incorrect as newborns typically show a preference for familiar voices, such as their mother's voice. Choice D is incorrect as newborns do not see unclearly across a wide range of distances; rather, their vision is clearer for nearby objects.

Correct Answer: B

Rationale: By using random assignment of participants to treatment conditions, investigators increase the chances that participants' characteristics will be equally distributed across treatment groups. Random assignment helps reduce the likelihood of bias in the selection process and ensures that any differences between groups are due to the treatment and not pre-existing group differences. Sequential, systematic, and correlational assignment methods do not provide the same level of assurance in distributing participants' characteristics equally across treatment groups.