Researchers Obtained the Data Depicted Here by Sampling Human Blood

Multiple Choice

Researchers obtained the data depicted here by sampling human blood containing HIV and then isolating and sequencing genes within the human immunodeficiency virus's DNA.What does the line and shaded area that intersect the x-axis represent?

A) an index of natural selection on the HIV genes studied
B) an index of mutations within gene regions of HIV that are unrelated to the success of the virus (such as how virulent it is or how well it reproduces within its human hosts)
C) a measurement of changes between HIV gene sequences,specifically on genes important for the replication,reproduction,and spreading of the virus
D) a prediction of when HIV first infected humans,based on the theory that neutral DNA mutations to non-protein coding sections of the HIV genome have accumulated in a consistent manner over time.