Which is the best example of a thesis statement for an argumentative essay about zoos and animal welfare?

1) Although many people feel that keeping animals captive in zoos is cruel, zoos are necessary for animal conservation and research.
2) Zoos have been around for thousands of years, and each year they draw millions of people to see the variety of animals they house.
3) Many animals die prematurely in zoos because they are exposed to infectious diseases.
4) Animals can be bred at zoos to increase their population and to combat extinction.