**Core Concept**
Pompe's disease is a rare genetic disorder caused by the accumulation of glycogen in the body due to a deficiency of a crucial enzyme involved in glycogen breakdown. This condition is characterized by progressive muscle weakness and cardiomegaly.

**Why the Correct Answer is Right**
The correct enzyme responsible for Pompe's disease is acid alpha-glucosidase (GAA), also known as acid maltase. This enzyme catalyzes the breakdown of glycogen into glucose in lysosomes. A deficiency of GAA leads to the accumulation of glycogen in lysosomes, causing cellular damage and death. This results in muscle weakness, cardiomegaly, and other systemic symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Pompe's disease is not caused by a deficiency of acid phosphatase, which is a different enzyme involved in the breakdown of nucleic acids and proteins.

**Option B:** This option is incorrect because Fabry disease is caused by a deficiency of alpha-Gal A, an enzyme involved in the breakdown of globotriaosylceramide.

**Option C:** This option is incorrect because Tay-Sachs disease is caused by a deficiency of hexosaminidase A, an enzyme involved in the breakdown of gangliosides.

**Option D:** This option is incorrect because Gaucher disease is caused by a deficiency of glucocerebrosidase, an enzyme involved in the breakdown of glucocerebroside.

**Clinical Pearl / High-Yield Fact**
Pompe's disease is a classic example of a lysosomal storage disorder, which is a group of genetic disorders caused by the accumulation of abnormal substances in lysosomes.

**Correct Answer:** C. Acid alpha-glucosidase (GAA)