Answer the following question given this paragraph: 

Early in the development of a human fetus, the skeleton is made entirely of cartilage. The relatively soft cartilage gradually changes to hard bone through ossification. This is a process in which mineral deposits replace cartilage in bone. At birth, several areas of cartilage remain, including the ends of the long bones in the arms and legs. This allows these bones to keep growing in length during childhood.


Q: Early in the development of a human fetus, the skeleton is made entirely of what?


A:
cartilage