"One indication that some commonly observed physical change linked to age is a product of secondary aging is that ."

It does not occur in all adults

Explanation:

One indication that some commonly observed physical change linked to age is a product of secondary aging is that it does not occur in all adults

some commonly observed physical change that is most times linked to aging is classified as a product of secondary aging because they might not be seen on some adults whom might be of the same age bracket with people who manifest those physical changes and this is because of the differences in body types and in some cases due to the health status and lifestyle of the individuals

i would say b probably