What is biodiversity?
the rapid disappearance of a species in an area
the total number of different species in an area
the rapid appearance of a species in an area
the total number of a single species in an area

The total number of different species in an area.

Explanation:

Bio means relating to life, and diversity means a wide range of different, in this case, organisms.

Biodiversity is describing what exists, not disappearances, or appearances.

So you can rule out:

the rapid disappearance of a species in an area and the rapid appearance of a species in an area.

Diversity means many, so that wouldn't mean just one single species.

Rule out:

the total number of a single species in an area.

That means the total number of different species in an area is the answer.

:)

b. the carbon cycle ensures living things have a source of hydrogen

the cost of mining is extremely low compared to the money earned from mining, creating income to improve the environment.