Final answer:
The Maldives (A) is the island republic in the Indian Ocean where you could dive and swim all day. It is a prime location for tourism with beautiful coral reefs and beaches, but faces environmental threats due to low elevation.
Step-by-step explanation:
The island republic you could "dive" and swim all day in the Indian Ocean mentioned in the question is A) Maldives. The Maldives is known for its beautiful atolls, over 1,200 small islands, and stunning coral reefs, which make it an excellent destination for diving and water sports. As a site of great natural beauty, tourism plays a crucial role in the Maldivian economy, with the first tourist resort having opened in 1972. However, the country faces significant environmental threats due to its low elevation, making it susceptible to the effects of climate change and potential flooding. To address environmental concerns, in 2008, the president of the Maldives announced a plan to purchase land in other countries to protect its population from the rising sea levels.