Correct Answer: C

Rationale: Option C provides the most thorough experimental design by including a control group. In the first round, varying sugar intake levels help explore the relationship between sugar consumption and test scores. In the second round, by having participants consume no sugar, the student can compare results to observe any changes due to sugar intake. This approach enhances the validity of the findings by accounting for potential confounding factors and better identifying causal relationships. Choice A is not ideal as it lacks a control group and does not compare the impact of sugar consumption. Choice B does not explore the effects of sugar consumption adequately as it does not include a group without sugar. Choice D does not allow for comparison between different sugar consumption levels, limiting the ability to draw meaningful conclusions.

Correct Answer: A

Rationale: The correct answer is A: Diastolic pressure. The bottom number in a blood pressure reading represents the diastolic pressure, which indicates the lowest pressure in the arteries when the heart is resting between beats. This value is important in understanding the overall health of the cardiovascular system. Choice B, Systolic pressure, is the top number in a blood pressure reading and represents the pressure in the arteries when the heart is contracting. Choice C, Pulse rate, refers to the number of times the heart beats in a minute. Choice D, Mean arterial pressure, is a calculated value using both systolic and diastolic pressures to provide an average pressure in the arteries during a cardiac cycle, but it is not the bottom number in a blood pressure reading.

Correct Answer: C

Rationale: The correct answer is the mitral valve, also known as the bicuspid valve. The mitral valve prevents blood from flowing back into the left atrium during ventricular contraction. The tricuspid valve is located between the right atrium and right ventricle, the pulmonary valve is between the right ventricle and the pulmonary artery, and the aortic valve is situated between the left ventricle and the aorta. Therefore, choices A, B, and D are incorrect as they are not related to preventing blood from entering the left atrium during ventricular contraction.

Correct Answer: B

Rationale: The tricuspid valve (right atrioventricular valve) prevents backflow into the right atrium when the right ventricle contracts. This valve ensures that blood flows in the correct direction, preventing regurgitation into the atrium. The pulmonary valve is responsible for preventing backflow into the right ventricle from the pulmonary artery. The mitral valve prevents backflow into the left atrium, and the aortic valve prevents backflow into the left ventricle from the aorta. Therefore, the correct answer is the tricuspid valve as it specifically addresses the scenario of backflow into the atrium during ventricular contraction.

Correct Answer: B

Rationale: Lipids are hydrophobic molecules that are soluble in nonpolar solvents like oils but insoluble in water. They consist of fats, oils, waxes, and steroids and play essential roles in energy storage, insulation, and cell membrane structure. Carbohydrates, proteins, and nucleic acids are not typically soluble in nonpolar solvents and do not exhibit the same hydrophobic characteristics as lipids. Carbohydrates are usually hydrophilic and soluble in water, proteins have both hydrophilic and hydrophobic regions but are not generally soluble in nonpolar solvents, and nucleic acids are polar molecules that are not known for their solubility in nonpolar solvents.