The term string is used for A. The underside of a stair B. Outer projecting edge of a tread C. A sloping member which supports the steps in a stair D. A vertical member between two treads

The correct answer is: C. A sloping member which supports the steps in a stair.

A stringer is a structural member that supports the treads and risers of a staircase. It is typically made of wood, steel, or concrete, and it runs along the sides of the staircase. The stringer is what gives the staircase its shape and support.

The other options are incorrect. Option A is the underside of a stair, which is called the soffit. Option B is the outer projecting edge of a tread, which is called the nosing. Option D is a vertical member between two treads, which is called a riser.