In vitro fertilization

Correct Answer: A

Rationale: Step-by-step rationale: 1. In vitro fertilization (IVF) is commonly used when a couple faces infertility issues. 2. IVF involves fertilizing an egg with sperm outside the body in a laboratory setting. 3. This method helps couples who struggle with conceiving naturally. 4. Choice A is correct as it aligns with the primary purpose of IVF for couples experiencing fertility problems. Summary: - Choice B is incorrect as preimplantation diagnosis is a separate procedure within IVF. - Choice C is incorrect as IVF is not primarily for observing early development but for assisting in conception. - Choice D is incorrect as the optimization of the fertilized egg is not the main goal of IVF, but rather achieving pregnancy for couples with fertility challenges.

Correct Answer: B

Rationale: The correct answer is B (50%). This is because empirical data shows that around half of Americans live in areas with poor air quality due to factors like pollution, industrial activities, and traffic congestion. Choice A (10%) is too low and underestimates the prevalence of poor air quality in the US. Choice C (75%) is too high and exaggerates the problem, as not three-quarters of Americans are affected. Choice D (90%) is also an overestimation, as the majority but not almost all Americans are impacted by poor air quality. Therefore, B is the most accurate representation of the proportion of Americans living in areas with poor air quality.

Correct Answer: C

Rationale: The correct answer is C: Evaporation and precipitation. These two processes are fundamental to the hydrological cycle. Evaporation is the process where water is converted from liquid to vapor and enters the atmosphere, while precipitation is when water vapor condenses and falls back to the Earth as rain, snow, sleet, or hail. This cycle is essential for maintaining Earth's water balance. A: Coagulation and sedimentation are processes used in water treatment to remove impurities, but they are not part of the hydrological cycle. B: Filtration and disinfection are also water treatment processes and do not directly involve the movement of water through the hydrological cycle. D: Chlorination and fluorination are methods used for water disinfection but do not play a role in the natural hydrological cycle.

Correct Answer: B

Rationale: The correct answer is B because air pollutants like sulfur dioxide and nitrogen oxides can mix with moisture in the air to form acidic compounds. When these acidic compounds dissolve in rainwater or dew, they can damage forests and buildings by causing corrosion, deterioration of materials, and harming plant life. Particulates (choices A and C) can physically damage surfaces but do not directly cause the chemical reactions that lead to harm. Dehydration of surfaces (choice D) is not a significant mechanism for the harm caused by air pollution to forests and buildings.

Correct Answer: D

Rationale: The correct answer is D because systematically treating animals with antibiotics can lead to the selection of pathogenic organisms that develop resistance to the drugs. This occurs due to the survival and proliferation of resistant strains when exposed to antibiotics, posing a significant threat to human health by potentially transferring these resistant genes to humans through food consumption. Choices A, B, and C are incorrect as raising the cost of meat, making animals sick, and developing resistance to drugs are not the primary concern associated with the misuse of antibiotics in animal agriculture.