Correct Answer: D

Rationale: In an experimental study examining whether the way angry encounters end affects children's emotional reactions, the dependent variable would be the children's emotional reactions. The dependent variable is the outcome being measured or tested in an experiment. In this study, the researchers are trying to understand how the way angry encounters end influences children's emotions. Therefore, the emotional reactions of the children would be the dependent variable that is being studied and measured in relation to the way angry encounters end. Choices A, B, and C are not the dependent variable in this scenario. While they may be related factors, the main focus of the study is on how the way angry encounters end impacts children's emotional reactions, making children's emotional reactions the dependent variable.

Correct Answer: D

Rationale: The correct answer is D because investigators who study development aim to identify the factors that influence consistencies and transformations in people from conception to death. This goal encompasses various domains such as physical, cognitive, emotional, and social development, highlighting the comprehensive nature of developmental research. Choices A, B, and C are incorrect as they do not align with the overarching goal of developmental researchers, which is to understand the factors influencing individuals throughout their lifespan, rather than focusing solely on genetic factors, environmental factors related to disease, or abnormal development in specific age groups.

Correct Answer: D

Rationale: The correct answer is D, isotretinoin. Isotretinoin is a medication commonly used to treat severe acne, but it is a potent teratogen, meaning it can cause severe birth defects if taken during pregnancy. Aspirin (choice A) is not a widely used potent teratogen. Diethylstilbestrol (DES) (choice B) was a known teratogen, but it is not currently widely used. Thalidomide (choice C) was another historical teratogen, but it is also not currently widely used. Therefore, isotretinoin is the most relevant answer as it is a commonly used medication that poses a high risk of birth defects if used during pregnancy.

Correct Answer: D

Rationale: Cross-sectional studies can be threatened by cohort effects because different age groups may have experienced different historical or social contexts, influencing the results. This disparity can lead to invalid comparisons between age groups, confounding the study's findings. Option A, practice effects, refer to changes in participants' behavior due to repeated testing, not a specific threat to cross-sectional studies. Participant dropout (Option B) is a threat related to attrition in longitudinal studies, not cross-sectional studies. Sequential timing (Option C) does not pose a threat to cross-sectional studies; instead, it refers to the order of tasks in a study design.

Correct Answer: B

Rationale: The correct answer is B: 'Helps keep the temperature of the prenatal world constant.' Amniotic fluid helps maintain a stable and warm environment for the developing organism, assisting in regulating the temperature. This fluid also acts as a cushion, protecting the fetus from physical harm. Choices A, C, and D are incorrect because while amniotic fluid provides protection and support to the developing organism, it does not directly deliver food, oxygen, nutrients, or remove waste products, nor does it produce blood cells as the organs eventually take over this function.