In a hairline fracture
a. the break is completely across the bone
b. the two parts of the bone do not separate
c. the bone shatters into more than two peices
d. one part of the bone protrudes through the skin

The answer is B. The two parts of the bone do not separate. 

Hairline fractures, or also called Stress Fractures are such fractures that occur from repeated stress over time, such as jumping. They are fatigue-induced and do not occur by a single severe trauma, but by repeated submaximal loading.

Hairline fractures are most commonly seen in the tibia, metatarsals and navicular bone.

It is hard to notice them on X-ray, and they mostly present as increasing weight bearing pain.

Why  do you think body composition focuses  on the  ratio  of  fatty tissue  to  other body tissue? why is  body composition not related  to  weight?

If you under eat, your bones will narrow.