**Core Concept**
The decalcification method is used to study oral tissue by removing the mineral content, typically calcium and phosphorus, from the tissue samples. This process allows for the examination of the tissue's cellular and histological structures without the interference of mineral deposits.

**Why the Correct Answer is Right**
The decalcification method is essential for studying oral tissue, particularly in the examination of teeth and bones. The process involves the use of chemical agents, such as formic acid or EDTA, which dissolve the calcium and phosphorus salts, allowing for the tissue to be sectioned and stained for microscopic examination. This method is particularly useful in the diagnosis of conditions such as osteomyelitis, periodontal disease, and tooth resorption.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the decalcification method, which is specifically used for the study of oral tissue.

**Option B:** While radiography is a diagnostic tool used in dentistry, it does not involve the decalcification of oral tissue.

**Option C:** Histopathology is a broader field of study that involves the examination of tissue samples, but it does not specifically relate to the decalcification method used in oral pathology.

**Clinical Pearl / High-Yield Fact**
The decalcification method is a critical step in the examination of oral tissue, allowing for the accurate diagnosis of various conditions affecting the teeth and bones. It is essential to use the correct decalcification agents and times to prevent tissue damage and ensure accurate results.

**Correct Answer: A. Study of oral tissue by decalcification method is useful for histopathological examination.**