**Core Concept**
Pyruvate, a key intermediate in glycolysis, can be converted into various products through different metabolic pathways. It serves as a substrate for several enzymes, enabling its participation in various biochemical reactions.

**Why the Correct Answer is Right**
Pyruvate is a versatile molecule that can be converted into acetyl-CoA, which then enters the citric acid cycle (Krebs cycle) through the action of the pyruvate dehydrogenase complex. Additionally, pyruvate can be converted into lactate through the action of lactate dehydrogenase, especially in anaerobic conditions. Furthermore, pyruvate can be converted into oxaloacetate through the action of pyruvate carboxylase, which is a key step in gluconeogenesis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pyruvate is indeed a substrate for the enzyme pyruvate kinase, which is involved in glycolysis.
**Option B:** This option is incorrect because pyruvate is a substrate for the enzyme pyruvate carboxylase, which is involved in gluconeogenesis.
**Option C:** This option is incorrect because pyruvate is a substrate for the enzyme lactate dehydrogenase, which is involved in anaerobic glycolysis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the conversion of pyruvate to lactate is a key adaptation to anaerobic conditions, allowing cells to generate energy in the absence of sufficient oxygen.

**Correct Answer:** D.