The following are subjects of interest to gerontologists:
a. young-old.
c. old-old.
b. middle-old.
d. all of the above.

D. All of the above.

Gerontology is the study social, cultural, psychological, cognitive, and biological aspects of aging. Likewise, gerontologists are healthcare specialists who work with elderly patients. They provide services to people in nursing homes, senior citizen centers, and other similar facilities. So, we can assume that a gerontologist would be interested in the process of aging and would work with young-old, middle-old, and old-old people.

heritage? culture? religion? gene? trait?

- "about the claims : -

making a claim is just a fancy way of saying that you're stating your main point.' claims are not just opinions. a claim tells what you think is true about a topic based on your knowledge .

about the country claims : -

a counterclaim is just the opposite of a claim. counterclaims are also provable and supportable by reasons and evidence. not just, 'because i said so.' when you're planning an argument, you need to know what the counterclaim might be so that you can make sure that you disprove it with your reasons and evidence your research." - (catherineroberts)