Mucous membranes?

A. Cover all the body's surfaces.

B. Line internal body surfaces that are in contact with the environment.

C. Produce antibodies to combat infection.

D. Secrete sweat, which has antibacterial enzymes.

Mucous membranes are the one which line internal body surfaces that are in contact with the environment. As examples we can say the nose musous membranes, the intern part of mouth, the genital organs. They are delicate and easily blees because they are highly irrigated by blood and as a consequence, produce mucous, which is a glicoprotein to impede the entrance of microorganisms (non-self), serving as a barrier.