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.