The correct answer is option 1: Glass snake. Glass snakes are not true snakes. They are lizards that resemble snakes due to their long, slender bodies and lack of legs. However, unlike snakes, they have eyelids and external ears.

Option 2: Sea snakes are true snakes that have adapted to living in marine environments. They are highly venomous and spend most of their lives in water.

Option 3: Tree snakes are also known as vine snakes or green snakes. They are true snakes that are adapted to living and climbing in trees.

Option 4: Blind snakes, also known as worm snakes, are true snakes that are small, burrowing reptiles. They are often mistaken for earthworms due to their similar appearance.

Therefore, the Glass snake is not a true snake, but a lizard that resembles a snake.