Question

For lineage a, how many speciation and extinction events occurred from 2 million years ago to time 0?

Answer 1

I found the problem.

Lineage a had 5 speciation events and 5 extinctions.

Speciation events are events that splits the lineage and produce two or more separate species.
Extinction events are events where the whole species die out in a short span of time. It is called "the great dying".

In the image,speciation is represented when one line breaks into two lines. Extinction is represented with the dagger symbol.