Answer:
(A) the estimated population
Step-by-step 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.