What are the main functions of steroids?

I- The most known steroid is cholesterol, which is present in the biological membranes of all cells except bacteria.
II- Steroids play different functions according to the chemical groups attached to their basic structure.
III- Steroids are only present in animals.
IV- Steroids are not essential in the diet, as the body can synthesize the necessary sugars from other molecules.
a) I and II are correct.
b) II and IV are correct.
c) I, II, and IV are correct.
d) Only III is incorrect.