The immature bone found in the fetus and during bone repair is:

A. edema
Edema involves fluid accumulation and can contribute to swelling and immune cell movement, but it does not directly wall off the injury site.

B. vasodilation of blood vessels
Vasodilation increases blood flow to bring immune cells and nutrients, but does not physically isolate the injury.

C. formation of a clot
A blood clot forms a physical barrier that helps prevent the spread of pathogens and walls off the injury.

D. all of the above
While A and B support inflammation and healing, only C directly achieves the goal of physically walling off the injured area. Therefore, "all of the above" is in

A. UV radiation
UV exposure stimulates melanocytes to increase melanin production, leading to tanning and darker pigmentation.

B. pregnancy
Hormonal changes during pregnancy, particularly estrogen and MSH, can increase pigmentation, such as in melasma (the "mask of pregnancy").

C. melanocyte stimulating hormone increased number of melanocytes
MSH stimulates melanin production, not the number of melanocytes. The number of melanocytes remains relatively stable in most individuals.

D. increased production of dark melanin
More production of eumelanin (dark melanin) leads to increased pigmentation, seen in individuals with darker skin tones or increased melanin activity.