Question

read the passage and then answer the question.
a typical human baby is born with around 300 bones, but by the time that baby reaches adulthood, it will have only 206. initially, such a notable diminution in the number of bones may seem counterintuitive—shouldn’t a skeleton need more bones, not fewer, as it grows? the explanation lies in the way bones grow and develop.
with age, the human skeleton undergoes a process of bone fusion. newborns’ bones are spongy and give way to pressure because they are made primarily of cartilage. these malleable bones make it easier for a newborn to pass through the narrow birth canal. over time, however, the bones gain more calcium and join together, forming the 206 bones that make up an adult’s skeletal structure.
what is the meaning of fusion as used in the passage?
chemistry
combining
softening
creation

Explanation:

The passage states that over time, a baby's separate bones join together to form the 206 bones of an adult skeleton. This joining process is defined as "bone fusion" here, which matches the meaning of combining.

Answer:

combining