The complete question goes like this :
Almost every major city in the world has a zoo. Humans have kept and enjoyed animals since the prehistoric times. Ancient Greeks and Romans kept small zoos. Over the past fifty years, zoos have changed remarkably. Today zoos provide the animals with larger and more natural habitats.
Which sentence could be added to the passage as a supporting detail?
The correct answer is A) Zoos also provide great research facilities
This sentence is adding more information directly related to the state of the zoo in modern times. Besides the educational and entertaining purposes, the zoos are now becoming important centres for research and places for developing conservation strategies for endangered animals. All of the other sentences are not relevant to the importance and characteristic of modern-day zoos.