The answer is E. Sharpener.
A book is a written or printed work consisting of pages fastened together and typically having a cover.
Paper is a thin, flexible material produced from cellulose fibers, used for writing or printing on, wrapping things, or making paper products.
A pencil is a writing implement consisting of a thin core of graphite enclosed in a wooden or metal casing.
A pen is a writing instrument consisting of a nib or ballpoint tip that holds ink and is used for writing or drawing.
A sharpener is a tool used to sharpen pencils.
The sharpener is the odd one out because it is the only tool that is used to sharpen other objects. The other four options are all objects that can be used for writing or drawing.