Africa's black rhino population in the mid-1970's numbered about 20,000, ten times the estimated population of 2,000 in 1997.

(A) the estimated population

(B) that of their estimated population

(C) more than the population's estimated amount

(D) more black rhinos than their population estimate

(E) more than that of their population's estimated amount

(A) the estimated population

Explanation:

The best way to deal with this is to avoid the plural pronoun ' their, ' which has no place in this sense as we're talking about the rhino (a singular) group.

Therefore options B and E are removed.

In terms of ' amount ' we do not quantify a population. Therefore, option C is also removed.

In D the estimation of population is odd.

The correct version is the projected population. A is the right choice.