Which is an organ?
a.) heart
b.) circulatory system
c.) blood
d.) muscle tissue

A) Heart

Explanation:

You know dâmΠ well blood is not an organ, it's a body liquid composed of blood cells suspended in blood plasma.

Muscle tissue is what makes a muscle. Note that tissue makes organs : )

Circulatory system:The system that moves blood throughout the body which is composed of the heart, arteries, capillaries, and veins.

That's it, hope this helps you ♡ ;)

A.) heart

Explanation:

Your heart is actually a muscular organ. An organ is a group of tissues that work together to perform a specific function. In the case of your heart, this function is pumping blood throughout your body. Additionally, the heart is largely made up of a type of muscle tissue called cardiac muscle.