**Core Concept**
Meat from different animal sources has varying fat contents, which affect their nutritional value and impact on health. This difference is crucial for understanding the potential risks associated with consuming high-fat meats.

**Why the Correct Answer is Right**
Beef generally contains a higher percentage of fat compared to other meats like chicken, fish, and mutton. This is due to the composition of beef, which often has a higher proportion of marbling (intramuscular fat) and a lower proportion of lean meat. The fat in beef can be both saturated and unsaturated, affecting its impact on cardiovascular health.

**Why Each Wrong Option is Incorrect**
**Option B:** Mutton, although slightly higher in fat than chicken, does not typically have the same level of marbling as beef, resulting in a lower overall fat content.
**Option C:** Chicken is generally a lean protein source, with a relatively low fat content compared to beef, especially when cooked without added fats.
**Option D:** Fish, particularly fatty fish like salmon, may have a higher fat content than chicken or mutton but significantly lower than beef, due to the varying types of fat present in fish.

**Clinical Pearl / High-Yield Fact**
When considering the fat content of different meats, it's essential to note that cooking methods can also impact the final fat content. Grilling or frying can increase the fat content of meats, whereas baking or broiling tends to retain more of the natural lean protein.

**✓ Correct Answer: A. Beef. Beef generally has the highest fat content among the given options.**