Correct Answer: B

Rationale: The correct answer is B: Circulatory. The circulatory system, made up of the heart, blood vessels, and blood, is responsible for transporting blood throughout the body. It plays a vital role in delivering oxygen, nutrients, hormones, and removing waste products from cells. The respiratory system, on the other hand, is responsible for gas exchange in the lungs. The nervous system transmits signals between different parts of the body, while the digestive system processes food and absorbs nutrients from it. Therefore, choices A, C, and D are incorrect as they are not primarily involved in the transportation of blood throughout the body.

Correct Answer: C

Rationale: The spleen is the correct answer. The spleen is a vital organ in the immune system responsible for filtering pathogens from the blood. It contains specialized immune cells that aid in recognizing and eliminating harmful substances. Additionally, the spleen plays a role in recycling old red blood cells. Choices A, B, and D are incorrect. Lymph nodes primarily filter lymph fluid, not blood. Kidneys are involved in filtering waste and regulating fluid balance, not specifically filtering pathogens from the blood. The pancreas functions in hormone regulation and digestion, unrelated to filtering pathogens from the blood.

Correct Answer: B

Rationale: The primary function of the kidneys is to filter blood and remove waste products from the body, producing urine in the process. This function helps in maintaining the body's internal environment stable, a process known as homeostasis. Option A, 'To digest food,' is incorrect as digestion primarily occurs in the gastrointestinal system, not in the kidneys. Option C, 'To absorb nutrients,' is also incorrect because nutrient absorption mainly takes place in the intestines. Option D, 'To transport oxygen,' is incorrect as the lungs and circulatory system are responsible for oxygen transport, not the kidneys.

Correct Answer: A

Rationale: The correct answer is A: Arteries. Arteries are the large blood vessels that carry blood away from the heart to various parts of the body. They have thick, muscular walls to withstand the high pressure generated by the heart's pumping action. Choice B, Arterioles, are smaller branches of arteries that further divide into capillaries. Choice C, Veins, carry blood back to the heart and have thinner walls compared to arteries. Choice D, Venules, are smaller veins that collect blood from capillaries and merge into larger veins.

Correct Answer: A

Rationale: The correct answer is Estrogen (Choice A). Estrogen is produced by the ovaries and is essential for the maturation of eggs. It plays a crucial role in the development of secondary sexual characteristics, regulation of the menstrual cycle, and preparation of the uterus for implantation of a fertilized egg. Luteinizing Hormone (Choice B) is released by the pituitary gland and plays a role in ovulation, not the maturation of eggs. Progesterone (Choice C) is produced by the ovaries after ovulation and is important for preparing the uterus for pregnancy, not maturing eggs. Testosterone (Choice D) is a male sex hormone primarily produced in the testes, and while small amounts are also produced in the ovaries, it is not the hormone responsible for maturing eggs.