Verified Answer :

Well, the thing is: we don't really know, as we don't even know how many species there are on earth.

If we take a look at the estimates of World Wide Fund for Nature, an organization that works toward combating species extinction, their estimates vary from 200 to 100 000 - but a probable number is 20 000 (d).

Answer:

d. 20000

Explanation:

It has been observed that over the years, species have been going extinct due to human reasons such as excessive hunting, environmental factors such as natural disasters, global warming and also due to changes in their genetic makeup or a reduced reproduction.

It has been estimated that every year 20,000 species are going extinct.