The correct answer is option 2, which means that 1, 2, and 3 are the national parks that have been declared as World Heritage by UNESCO.

Let`s analyze each option to understand why option 2 is the correct answer:

Option 1 states that only Keoladeo National Park and Sundarbans National Park are declared as World Heritage by UNESCO. This option is incorrect because it does not include Kaziranga National Park, which is also a World Heritage site.

Option 3 suggests that only Kaziranga National Park and Ranthambore National Park are declared as World Heritage by UNESCO. This option is incorrect because it does not include Keoladeo National Park and Sundarbans National Park, both of which have been recognized as World Heritage sites.

Option 4 states that all four national parks, Keoladeo National Park, Sundarbans National Park, Kaziranga National Park, and Ranthambore National Park, are declared as World Heritage by UNESCO. This option is incorrect because Ranthambore National Park has not been declared as a World Heritage site by UNESCO.

Therefore, the correct answer is option 2, which includes all the national parks that have been declared as World Heritage sites by UNESCO: Keolade