Correct Answer: C

Rationale: The best-known effect of smoking during the prenatal period is low birth weight. Smoking during pregnancy is a known teratogen that can lead to negative outcomes for the developing fetus, such as growth restrictions resulting in low birth weight. This condition can have significant long-term consequences on the child's health and development. Choices A, B, and D are incorrect as they are not the primary effect associated with smoking during the prenatal period. Colic is typically associated with digestive issues, respiratory distress at birth can be caused by various factors other than smoking, and delayed language development is not directly linked to smoking during pregnancy.

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: 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: 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 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.