The snake species that has a diet mainly composed of other snakes is Option 4: King cobra (Ophiophagus hannah). The King cobra is a large and highly venomous snake native to Southeast Asia, and it is well-known for its specialized diet of other snakes.

Here are some detailed reasons supporting this choice:

1. Snake Diet: The King cobra`s diet primarily consists of other snakes, making it an ophiophagous species (snake eater). While it can consume other prey items such as lizards, birds, and rodents, snakes are its preferred and most common food source. This dietary preference sets it apart from the other options provided.

2. Adaptations: The King cobra is specially adapted to hunt, overpower, and consume other snakes. It has a potent venomous bite that is particularly effective against other reptiles, including snakes. Its venom contains neurotoxins that can quickly incapacitate and kill its prey, allowing it to consume even larger snakes.

3. Size and Feeding Habits: King cobras are the longest venomous snakes in the world, reaching lengths of up to 18 feet (5.5 meters). This size advantage enables them to tackle larger snake species that would be too formidable for most other snakes. They have a flexible jaw structure and expandable throat that allows them to swallow their prey whole, even if the prey is larger than their own body diameter.

4. Known Prey: Observations and studies have documented the King cobra preying on various snake species, including pythons, cobras, rat snakes, and even other venomous snakes. This consumption of other snakes is well-documented in their natural habitat, providing evidence of their specialized diet.

It`s worth noting that while the other snake species listed in the options may also consume other snakes as part of their diet, the King cobra stands out as the species whose diet is mainly composed of other snakes. Its preference for snake prey and its adaptations for capturing and consuming snakes make it a specialized ophiophagous snake.