The correct answer is option 4, Silk. Silk is considered as the strongest natural fiber. Cotton, option 1, although a natural fiber, is not as strong as silk. Jute, option 2, is known for its strength, but it is a vegetable fiber and not a natural fiber. Wool, option 3, is also a natural fiber, but it is not as strong as silk. Silk is known for its strength and durability, making it one of the strongest natural fibers available. It is produced by silkworms and is known for its lustrous appearance and smooth texture. Silk fibers are also known to have good tensile strength and elasticity, making them ideal for various applications such as clothing, upholstery, and parachutes.