**Core Concept**
Creatinine kinase (CK) is an enzyme found in various tissues, including skeletal muscle, heart, brain, and smooth muscle. There are three main isoforms of CK: CK-MM (muscle-type), CK-MB (brain-type), and CK-BB (brain-type). Each isoform has specific tissue distribution and clinical implications.

**Why the Correct Answer is Right**
CK-MM is predominantly found in skeletal muscle and is responsible for energy transfer during muscle contraction. Elevated CK-MM levels are seen in conditions affecting skeletal muscle, such as muscle injury, inflammation, or disease. In contrast, CK-MB is primarily found in cardiac muscle and is associated with myocardial damage or infarction. CK-BB is found in smooth muscle, brain, and other tissues. The specific isoform increase depends on the underlying pathology.

**Why Each Wrong Option is Incorrect**
**Option A:** Elevated CK-BB levels are seen in brain injury or disease, not skeletal muscle conditions.
**Option B:** CK-MB is associated with cardiac muscle damage, not skeletal muscle conditions.
**Option C:** Elevated CK-MM levels are not typically seen in liver disease.

**Clinical Pearl / High-Yield Fact**
Remember that CK-MM is a useful marker for skeletal muscle damage, whereas CK-MB is more specific for cardiac muscle damage.

**Correct Answer:** D.