What prevents backflow of blood inside the heart during contraction?

The correct answer is A) Heart.

Hint – Blood flow in the heart is unidirectional in both the right and left chambers. Flaps like structure sustain the unidirectional flow.

Part One: The Heart

The heart is a blood pumping organ that uses the circulatory system’s blood arteries to circulate blood throughout the body.
The right and left sides of the heart are separated. There is one atrium (upper chamber) and one ventricle (bottom heart) in each half.

Valves (Part 2)

Between the chambers of the atrium and ventricle are valves that prevent blood from flowing backward.
The Tricuspid valve is located between the right atrium and the right ventricle.
The Bicuspid valve is located between the left atrium and the left ventricle.
Between the ventricles and the pulmonary artery and the systemic aorta is the semilunar valve.

Part 3: Final Thoughts

The four valves of the heart prevent blood from flowing backward within the heart.
The strong muscular wall of the ventricles (particularly the left ventricle) aids in the pressure-driven delivery of blood to the whole body.
Atria has a thinner wall than ventricles since they just have to pump blood to the ventricles and not the rest of the body.

Last but not least, the heart’s valves prevent blood from flowing backward within the heart.