Why are fibrous proteins important as structural molecules both within cells and extracellularly?

Fibrous proteins are important as structural molecules that are elongated in shape and are found within cells and extracellularly because they are used to construct tendons, ligaments and muscle fibers that are in the body as connective tissues. These proteins are physically very tough that they can be stretchy or supple. These proteins are known to have a low solubility in water as compared to globular proteins. There are two special type of this protein namely alpha keratin and collagen. Alpha keratins are found in the structures of finger nails and hair. Collagen, on the other hand, are located in tendons, bone and cartilage. 

The answer is probably c. xylem