What type of hair covers the entire body of fetuses?

The correct answer is lanugo, which refers to the fine, soft hair that covers the entire body of a fetus during gestation. This hair is typically very light and downy, serving as a protective layer while the fetus develops in the womb. Lanugo usually begins to shed in the later stages of pregnancy and is mostly gone by the time of birth, although some newborns may retain a small amount.

Terminal hair is coarser, thicker hair that develops later in life, typically during puberty, and is found in areas such as the scalp, face, and body. Vellus hair, on the other hand, is fine, short, and usually unpigmented hair that is present on most of the human body after birth. Both terminal and vellus hair serve different purposes and develop at different stages of life compared to lanugo. Thus, the identification of lanugo as the type of hair covering the fetus is accurate, as it uniquely characterizes this developmental phase.