[I picked d.]

Question

How many species are estimated to be living on earth?
a.between 10,000 and 1,000,000
b.between 500,000 and 1 million
c.between 1 and 5 million
d.between 10 and 50 million

http://faculty.plattsburgh.edu/thomas.wolosz/howmanysp.htm

This is a political, not scientfic number. The more species one has, the more become endangered. d is probably the most cited number in political circles, but upwards to 200 million are commonplace in scientific estimates.