**Core Concept**
Porcelain fused to metal (PFM) crowns involve a metal substructure covered with a layer of porcelain for aesthetic and durability purposes. The porcelain used in PFM crowns must have certain properties to ensure a strong bond with the metal substructure and to maintain its aesthetic appeal.

**Why the Correct Answer is Right**
The correct answer is **translucency**. The porcelain used in PFM crowns should be translucency to allow light to pass through and give the appearance of natural teeth. This is achieved by using a specific type of porcelain that has a high degree of translucency. The translucency of the porcelain helps to create a natural appearance of the tooth, making it difficult to distinguish from a natural tooth. This is particularly important in the anterior region of the mouth where aesthetics are a major concern.

**Why Each Wrong Option is Incorrect**
**Option A:** **Strength** - While strength is an important property of porcelain used in PFM crowns, it is not the primary property that is being tested in this question. The porcelain should have a balance of strength and translucency.

**Option B:** **High Fusing Temperature** - The fusing temperature of the porcelain is not directly related to its suitability for use in PFM crowns. The fusing temperature is more related to the firing process in the dental laboratory.

**Option C:** **High Alumina Content** - The aluminous content of the porcelain is not directly related to its translucency or suitability for use in PFM crowns. Alumina is often used to improve the strength of porcelain.

**Clinical Pearl / High-Yield Fact**
When selecting a porcelain for PFM crowns, it is essential to consider the translucency of the porcelain to achieve a natural appearance. A porcelain with high translucency will give the appearance of a natural tooth, making it an essential property for aesthetic restorations.

**Correct Answer:** C.