**Core Concept**
Muscle hybridity refers to the presence of more than one type of muscle fiber within a single muscle. This phenomenon is crucial in understanding muscle physiology and pathology, particularly in the context of exercise and muscle disease.

**Why the Correct Answer is Right**
Hybrid muscles contain a mix of fast-twitch (FT) and slow-twitch (ST) muscle fibers, whereas non-hybrid muscles are composed of a single type of fiber. The distinction between hybrid and non-hybrid muscles is essential in understanding their function and response to various stimuli.

**Why Each Wrong Option is Incorrect**
**Option A:** Not all muscles are hybrid; many are non-hybrid, composed of a single type of fiber. For example, the soleus muscle is primarily composed of slow-twitch fibers and is not considered a hybrid muscle.
**Option B:** Some muscles may appear hybrid but are actually composed of a mix of different fiber types within a single fascicle. This does not mean they are entirely non-hybrid.
**Option C:** While it is true that some muscles have a higher proportion of one fiber type over another, this does not necessarily mean they are non-hybrid. Hybrid muscles can have a variable distribution of fiber types.

**Clinical Pearl / High-Yield Fact**
Understanding muscle hybridity is crucial in the context of exercise and muscle disease. Hybrid muscles are more resistant to fatigue and are better suited for high-intensity, short-duration activities, such as sprinting.

**Correct Answer: A. Soleus muscle**