Which coarse fabric is stiffened with glue to achieve a firm texture?

The choice of buckram as the coarse fabric that is stiffened with glue to achieve a firm texture makes sense due to its specific properties and applications. Buckram is traditionally made from cotton or linen and is treated with a starch or similar adhesive to provide rigidity. This characteristic allows it to hold its shape well, making it ideal for uses in bookbinding, hat making, and providing structural support in various textile crafts.

Conversely, the other fabric options do not share this property. Batiste is a lightweight and soft fabric typically used for garments and delicate items, while muslin is a plain weave fabric that is soft and flexible, commonly used for pattern making or as a base in projects. Denim, being a durable cotton twill fabric, is known for its strength and is usually used in clothing, but it does not have the stiff quality provided by glue treatment. Thus, buckram stands out for its intentional stiffening process, making it the correct answer.