**Core Concept**
The linear coefficient of thermal expansion (CTE) is a critical property of materials used in dental restorations, such as silver amalgam, which affects their performance and longevity. The CTE is a measure of how much a material expands or contracts in response to temperature changes.

**Why the Correct Answer is Right**
The silver amalgam restoration has a relatively low linear coefficient of thermal expansion, which is close to that of tooth enamel. This property allows the amalgam to contract and expand in a manner similar to the tooth, minimizing the risk of restoration failure due to thermal stress. The low CTE of silver amalgam is due to its composition, which includes a mixture of silver, tin, copper, and mercury. The mercury in the amalgam plays a crucial role in achieving the desired CTE.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the linear coefficient of thermal expansion of silver amalgam is not as high as some other dental materials, such as composite resins.
* **Option B:** This option is incorrect because the CTE of silver amalgam is not as low as that of some other materials, such as gold alloys.
* **Option C:** This option is incorrect because the CTE of silver amalgam is not as variable as that of some other materials, such as ceramic restorations.

**Clinical Pearl / High-Yield Fact**
A key factor to remember when selecting a dental restoration material is its linear coefficient of thermal expansion. A material with a CTE close to that of tooth enamel is generally preferred to minimize the risk of restoration failure due to thermal stress.

**Correct Answer: C. 15-18 x 10^(-6) per °C.**