Explanation:

- The Marine Conservation Society is raising awareness about Olive Ridley turtles with their festival.

- Olive Ridley turtles are named for their olive-colored shells.

- These turtles typically grow up to two feet in length.

- The turtles are known to mate around 1000 kilometers away from a specific location.

- They visit the beach to lay their eggs.

Now, let's look at the options for blank No. (4):

1. Festival - This doesn't correctly fit; it's where people gather, not where turtles mate.

2. Beach - A suitable ending phrase but not a mating location.

3. Sea - A suitable environment for mating but lacks specificity.

4. Sand - It refers more to laying eggs than mating.