The main type of muscle tissue among the options you provided is Cardiac muscle.
To clarify:
- Cardiac muscle is one of the three main types of muscle tissue (the others being skeletal and smooth muscle) and is found in the heart.
- Skin is an organ consisting of multiple tissue types, including epithelial and connective tissues.
- Spongy bone is a type of connective tissue.
- Blood vessels are structures made up of various types of tissues, including smooth muscle tissue, but are not a type of muscle tissue themselves.
So, the correct answer is Cardiac.