To better comprehend the magnitude of current extinctions, it ...

[penza]

To better comprehend the magnitude of current extinctions, it will be necessary to
A) monitor atmospheric carbon dioxide levels more closely.
B) differentiate between plant extinction and animal extinction numbers.
C) focus on identifying more species of mammals and birds.
D) identify more of the yet unknown species of organisms on Earth.
E) use the average extinction rates of vertebrates as a baseline.

[plus1]

I recall doing this last year, it's D, bye bye!

[penza]

Thanks so much!