**Core Concept**
Gracey curettes are a type of area-specific dental instrument used in periodontal therapy. They are designed to remove specific amounts of calculus and plaque from the tooth surface, while minimizing damage to the surrounding periodontal tissues.

**Why the Correct Answer is Right**
Gracey curettes are area-specific because they have different blade lengths and angles, allowing for precise removal of calculus in specific areas of the tooth. The design of Gracey curettes enables the removal of calculus from areas such as the mesial aspects of molars, the interproximal areas between teeth, and the distal aspects of molars. This specificity is due to the unique shape and design of the blade, which allows for precise access to these areas.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Gracey curettes are not designed for general-purpose calculus removal, but rather for specific area removal.
**Option B:** This option is incorrect because Gracey curettes are not interchangeable with other types of curettes, such as universal or sickle-shaped curettes.
**Option C:** This option is incorrect because Gracey curettes do not have interchangeable blades, but rather are designed with specific blade shapes and sizes for each area of the tooth.

**Clinical Pearl / High-Yield Fact**
When using Gracey curettes, it's essential to choose the correct instrument for the specific area of the tooth being treated, as using the wrong instrument can lead to damage to the periodontal tissues or incomplete removal of calculus.

**Correct Answer:** A.