question: Silk and cotton are examples of what kind of fiber?
distractor3: simple
distractor1: pure
distractor2: artificial
correct_answer: natural
support: The fibers that compose the materials for our clothes are either natural or human-made. Silk and cotton would be examples of natural fibers. Silk is produced by the silkworm and cotton is grown as a plant. Human-made fabrics include nylon, orlon, and a number of other polymers. These materials are made from hydrocarbons found in petroleum products. Synthetic polymers are also used in shoes, raingear, and camping items. The synthetic fabrics tend to be lighter than the natural ones and can be treated to make them more water-resistant and durable.