A(n) is a thick film of protein secreted by mucous membranes in the mouth that coats teeth and provides a substrate for Stretptococcus mutans to adhere and begin the formation of a slime layer.

The correct answer is - the biofilm.

Explanation:

Biofilms are a type of one or more than one type of microbes that grow on many different surfaces, These microbes include fungi, bacteria, and protist that develop attached to the surface and one another and embedded in a self-produced matrix.

It is a thick film of protein such as fibrin, polysaccharides such as alginate or eDNA secreted by the bacteria, and other microbes that cover the teeth surface.