Answer: D. The conjuctiva.
Explanation:
The conjuctiva is a membrane that lines the inside of the eye. Its function is to lubricate the surface of the eye, preventing it from dryness.
In trachoma, the conjuctiva becomes dry, scarred and this prevents it from performing its function of lubricating the eye. Trachoma can be treated but if left untreated, it can lead to blindness.