ANS:A - glass fibre in a polymer matrix.

Fiberglass is a composite material of glass fiber in a polymer matrix. Glass fibers, which are typically made from molten glass drawn into fine fibers, provide the reinforcing component of fiberglass. These fibers are combined with a polymer matrix, usually a thermosetting resin such as epoxy, polyester, or vinyl ester. The polymer matrix holds the glass fibers together and provides structural support, while the glass fibers impart strength, stiffness, and other mechanical properties to the composite material. So, the correct option is: glass fiber in a polymer matrix.