What happens when atp supplies energy for thin filaments in a muscle fiber to slide over the thick filaments?
a. the muscle contracts
b. the muscle relaxes
c. the muscle both contracts and relaxes
d. the muscle neither contracts nor relaxes
hair would be dry and brittle without the presence of
a. sebaceous glands
b. keratin
c. melanin
d. fat
compared with the walls of arteries the walls of capillaries
a. are thicker
b. are thinner
c. lack valves
d. have more resistance

2. A. Sebaceous glands
Lipids are macromolecules which provide insulation. 
A macromolecule is a large molecule. There are four groups of macromolecules: carbohydrates, proteins, nucleic acids and lipids. Lipids consist of glycerol and fatty acids and are constructed from fats, oils, waxes, phospholipids and steroids. A lipid's function is to insulate the body and provide warmth in cold conditions. It can be concluded that a person with very little body fat gets very cold easily and a person with a lot of body fat gets very warm very quickly.

3. B. Thinner