Phospholipids tend to group together so that their polar parts face the surrounding aqueous environment, while their hydrophobic tails face each other. the resulting structures are called
multiple choice
a. steroids
b. micelles
c. ketones
d. round cells

b. micelles

Explanation:

Phospholipids are lipids that contain a polar part, which is hydrophilic (i.e. likes water) and a non-polar part, which is hydrophobic (i.e. dislikes water).

When phospholipids are in an aqueous environment they form a structure called micelle, in which the polar heads face the water molecules and surround the non-polar tails which remain on the inside. This way, the polar heads protect the hydrophobic chains from exposure to the aqueous environment.

I've attached an image of a micelle for better understanding of its structure.