In National Parks, genetic diversity is maintained by:

1. A

   In-situ conservation

   In-situ conservation. This approach protects species within their natural habitats, such as National Parks and wildlife sanctuaries, allowing genetic diversity to be naturally maintained through ongoing evolutionary processes.

2. B

   Ex-situ conservation

   Ex-situ conservation. This option claims that genetic diversity is maintained outside natural habitats, such as in botanical gardens or zoos, which is secondary rather than primary for National Parks.

3. C

   Gene pool

   Gene pool. This refers to the total collection of different genes in an interbreeding population rather than the method or strategy of conservation used inside National Parks.

4. D

   None of the above

   None of the above. This option incorrectly assumes that none of the valid conservation strategies listed in the preceding choices apply to maintaining genetic diversity.

Summary. Official key is (a) In-situ conservation. National Parks are classic examples of in-situ conservation where entire ecosystems and their resident species are protected in their native environments. This method ensures that populations continue to evolve and adapt under natural conditions, preserving genetic diversity. Ex-situ methods like seed banks or zoos complement this but are not the primary mechanism within National Parks. Therefore, option (a) is the correct and comprehensive answer.