Sentence Correction

Africa’s black rhino population in the mid- 1970’s numbered about 20,000, ten times the estimated population of 2000 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 populations estimate
E.) more than that of their population’s estimated amount.

A
why not B

Because its too wordy
10 times A is 10xA and is exactly what the sentence intends.
10 times 2000 = 20000

in B [their] doesn't have a preceding referent... the OQ refers to black rhino population [singular] hence A

satish.nagdev wrote:in B [their] doesn't have a preceding referent... the OQ refers to black rhino population [singular] hence A

yes, there is no referent for "their" and it doesn't mean more than in the actual sentence, it is 10 times....
hence A