Which of the following is used for reinforcing concrete and comes in sheets?

Welded wire reinforcement is used for reinforcing concrete and is available in sheets. It consists of a grid of steel wires that are welded at intersections, providing structural support to prevent cracking and improve the tensile strength of concrete. This form of reinforcement is particularly useful in applications where a uniform distribution of strength is required across large surfaces, such as slabs, pavements, and walls.

Fiberglass mesh, while it may also be used in some applications for concrete reinforcement, is not typically formed in sheets large enough to be directly comparable to welded wire reinforcement. Plastic sheeting is primarily used as a vapor barrier or for ground cover, rather than as a structural reinforcement material. Wood fiber board does not serve a purpose in concrete reinforcement; rather, it is used for insulation or as a substrate in construction. Thus, welded wire reinforcement stands out as the correct answer due to its specific design and function in reinforcing concrete effectively.