Write a short paragraph describing the role of all four types of lipids: fats, phospholipids, waxes, and steroids.

Fats store energy, provide insulation and protect our vital organs. Phospholipids are an essential component of the cell membrane and play a key role in controlling the entry and exit of molecules and ions. Waxes are produced by many organisms as a protective layer against the outside environment, and can be used for example providing waterproofing to bird feathers. Steroids have various functions for maintaining homeostasis within organisms. 

The answer would be sand and gravel