Introduction:
In this analogy, we are given the relationship between "linen" and "flax" and we need to identify a similar relationship between two other terms. The relationship between "linen" and "flax" is that linen is a fabric made from flax fibers. We need to find a term that represents a fabric made from cotton fibers.

Explanation:
The correct answer is option D: Denim.

Linen and Flax:
- Linen is a type of fabric.
- Flax is a plant from which linen is made.
- Linen is derived from the fibers of the flax plant.
- Flax fibers are spun into yarn and then woven to create linen fabric.

Cotton and Denim:
- Cotton is a type of plant.
- Denim is a fabric made from cotton fibers.
- Cotton fibers are spun into yarn and then woven to create denim fabric.
- Denim fabric is known for its durability and is commonly used in the production of jeans and other clothing items.

Similarity between Linen:Flax and ? : Cotton:
- The relationship between linen and flax is that linen is made from flax fibers.
- Similarly, the relationship between cotton and denim is that denim is made from cotton fibers.
- Therefore, the correct answer is D: Denim, as it represents a fabric made from cotton fibers, just like linen represents a fabric made from flax fibers.

Conclusion:
In this analogy, the relationship between linen and flax is that linen is made from flax fibers. The correct answer, denoting a fabric made from cotton fibers, is denim.