**Core Concept**
Gluconeogenesis is a metabolic pathway that generates glucose from non-carbohydrate sources, such as amino acids, lactate, and glycerol. This process is crucial for maintaining blood glucose levels, especially during fasting or starvation.

**Why the Correct Answer is Right**
The correct answer is a compound that cannot be converted into glucose through gluconeogenesis. This is because gluconeogenesis involves the conversion of certain substrates into glucose through a series of enzyme-catalyzed reactions. Key enzymes involved in gluconeogenesis include glucose-6-phosphatase, fructose-1,6-bisphosphatase, and pyruvate carboxylase.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is a gluconeogenic precursor, which means it can be converted into glucose through gluconeogenesis.
**Option B:** This option is a non-gluconeogenic amino acid that cannot be converted into glucose.
**Option C:** This option is a gluconeogenic precursor that can be converted into glucose through gluconeogenesis.
**Option D:** This option is a compound that can be converted into glucose through gluconeogenesis.

**Clinical Pearl / High-Yield Fact**
The key to identifying non-gluconeogenic compounds is to recognize those that cannot be converted into glucose through gluconeogenesis. This includes certain amino acids, such as asparagine and glutamine, which are non-essential and can be synthesized from other compounds.

**Correct Answer: B. Alanine is not gluconeogenic.