Explain the concept of antagonistic muscles and identify the correct statement regarding their function.

Antagonistic muscles work in opposition to each other. When one muscle contracts, the other relaxes.

• Step 1: Understand the definition of antagonistic muscles. Antagonistic muscles are pairs of muscles that produce opposite movements at a joint. For example, the biceps and triceps in the arm.
• Step 2: Evaluate the given options.
  • A. contract at the same time: This is incorrect. If both contracted, movement would be restricted or they would work against each other.
  • B. do not contract at the same time: This is correct. When one contracts to cause movement, the other relaxes to allow that movement.
  • C. both muscles become thick when the arm is extended: This is incorrect. When the arm is extended, the triceps contract (become thick) and the biceps relax (become thin).
  • D. both muscles become thin when the arm is extended: This is incorrect. As explained above, the triceps contract and become thick.

The correct statement is that antagonistic muscles do not contract at the same time.

The final answer is $\boxed{\text{B}}$

The question asks which blood vessel supplies blood to the kidneys.

• Step 1: Identify the organ in question, which is the kidneys.
• Step 2: Recall the terminology for blood vessels associated with the kidneys. The prefix "renal" refers to the kidneys. Arteries carry blood to an organ, and veins carry blood away from an organ.
• Step 3: Evaluate the options.
  • A. renal artery: This vessel carries oxygenated blood from the aorta to the kidneys.
  • B. renal vein: This vessel carries deoxygenated blood away from the kidneys to the inferior vena cava.
  • C. hepatic artery: This vessel supplies blood to the liver.
  • D. hepatic portal vein: This vessel carries nutrient-rich blood from the digestive organs to the liver.

Therefore, the renal artery supplies blood to the kidneys.

The final answer is $\boxed{\text{A}}$

The question asks which of the following is not an importance of breathing through the nose. Only option A is visible.

• Step 1: Analyze the visible option.
  • A. traps dust: The nose contains hairs and mucus that effectively trap dust particles, preventing them from reaching the lungs. This is an important function of breathing through the nose.

Since the question asks for what is not an importance, and "traps dust" is an importance, option A cannot be the correct answer. To fully answer this question, the other options (B, C, D) are needed to identify the statement that is not an importance of nasal breathing.