Final answer:
Blood in the right ventricle arrives from the right atrium, passing through the tricuspid valve.
Step-by-step explanation:
The blood in the right ventricle arrived there from the right atrium. This flow of blood occurs through the tricuspid valve, which is designed to allow blood to move from the right atrium to the right ventricle. It is important to understand that this valve is one-way, preventing blood from flowing back into the atrium when the ventricle contracts. Furthermore, the mitral valve is associated with the left side of the heart, not the right, and allows blood to flow from the left atrium to the left ventricle. Consequently, the correct answer to the question would be option A: the right atrium.