Dr. Dawson is conducting a study with military veterans from the Vietnam and Gulf wars. He plans to evaluate them every year for 10 years to see if those with PTSD have a more pronounced decline in mental abilities and overall memory. This is a(n) study.

Longitudinal study

Explanation:

Longitudinal study is the study in which same variables are studied and analyzed over a long of short duration of particular tie.This study is used in surveys and research to determines pattern, trends, flow etc of different fields.

According to the question, Dr. Dawson is conducting a longitudinal study for researching on military veterans over 10 years of time period to determine the degradation of mental skills and ability persisting PTSD.

well, there are a lot of places we get information about earth from. like science classes, websites, books, newspapers, etc.

the answer is d.index