The blood circulatory system of vertebrates consists of

Analyze the question: It asks for the complete set of main components that make up the blood circulatory system in vertebrates.

Explain the concept: The circulatory system has three main parts:

1. Blood, the transport fluid.
2. The heart, the pump that drives blood around the body.
3. Blood vessels, the tubes that carry blood. There are three types of vessels: • Arteries carry blood away from the heart. • Capillaries are tiny vessels where exchange of materials happens between blood and tissues. • Veins carry blood back to the heart.

Step-by-step solution:

• Option B: The aorta is just one specific artery (the largest), so listing it leaves out the other arteries. It is too specific.
• Option C: It lacks capillaries, so the link between arteries and veins is missing.
• Option D: The vena cava is just one specific vein, so listing it is too specific. It also lacks capillaries.
• Option A: It lists the heart and all three general types of vessel (arteries, capillaries and veins). This is the complete and general answer.

Answer: A. heart, arteries, capillaries and veins

Exam tip: When an option names a specific structure (like the aorta or vena cava) and another names the general category (arteries or veins), the general category is usually the right choice for a question about "the system". Remember the chain: Heart → Arteries → Capillaries → Veins → Heart.