Question

Every year _______ species go extinct.
a. 3
b. 72
c. 1000
d. 20000

Answer 1

Every year 20000 species go extinct. C.20000

Answer 2

We can make an estimate however we don't know exactly what's out there!

Sources- 

WWF (Very well known) say about 10,000

So... it's between C and D but I would lean towards D.
But we definitely know it is not A or B!