Africa's black rhino population in the mid-1970's numbered about 20,000, ten times the estimated population of 2,000 in 1997.
the estimated population
that of their estimated population
more than the population's estimated amount
more black rhinos than their population estimate
more than that of their population's estimated amount
不说the amount of population或population's amount, 可以直接说population is 2000;number做动词表示总数达到,总计为
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