**Core Concept**
Digestive enzymes are proteins that catalyze the breakdown of complex molecules into simpler substances, facilitating nutrient absorption in the gastrointestinal tract. These enzymes are produced by various glands and organs within the digestive system, each with specific functions and optimal pH ranges.

**Why the Correct Answer is Right**
The correct answer is that all digestive enzymes are **proteins**. This is because enzymes are biological catalysts that speed up chemical reactions, and proteins are the primary macromolecules that can perform this function in the digestive system. Proteins have a unique three-dimensional structure that allows them to bind to specific substrates, positioning them for optimal catalysis. The primary function of digestive enzymes is to break down carbohydrates, proteins, and fats into their constituent monomers, which can then be absorbed and utilized by the body.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too broad and nonspecific. While many digestive enzymes are indeed **lipid-soluble**, not all of them are. Some enzymes, such as amylase and lactase, are water-soluble and operate in the aqueous environment of the digestive tract.
**Option B:** This option is incorrect because **inorganic compounds** are not typically associated with enzymatic activity in the digestive system. Enzymes are proteins that catalyze chemical reactions, and inorganic compounds do not possess this ability.
**Option C:** This option is incorrect because **carbohydrates** are the substrates broken down by some digestive enzymes, such as amylase and sucrase, but not all digestive enzymes are carbohydrate-based.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that digestive enzymes are **pH-dependent**, meaning they operate optimally within a specific pH range. For example, pepsin, a digestive enzyme produced in the stomach, operates optimally at a pH of 2, while amylase, produced in the small intestine, operates optimally at a pH of 7.

**Correct Answer: C. Proteins.