Which muscles act involuntarily?
(i) Striated muscles (ii) Smooth muscles
(iii) Cardiac muscles (iv) Skeletal muscles

Options

A. (i) and (ii)
B. (ii) and (iii)
C. (i) and (iv)
D. (iii) and (iv)

Explanation

To determine which muscles act involuntarily, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Muscle Types**:
- Muscles are categorized into three main types: skeletal (or striated), smooth, and cardiac muscles.

2. **Define Voluntary vs. Involuntary Muscles**:
- Voluntary muscles are those that can be controlled consciously (e.g., moving your arms or legs). In contrast, involuntary muscles are not under conscious control (e.g., muscles in the heart and digestive organs).

3. **Identify Skeletal Muscles**:
- Skeletal muscles are attached to bones and are responsible for voluntary movements. They have a striated appearance under a microscope. Therefore, they are not involuntary.

4. **Identify Smooth Muscles**:
- Smooth muscles are found in internal organs (like the stomach and intestines) and are not striated. They operate involuntarily, meaning we cannot consciously control them.

5. **Identify Cardiac Muscles**:
- Cardiac muscles are found only in the heart. They have a striated appearance similar to skeletal muscles, but they are also involuntary, as we cannot consciously control the heartbeat.

6. **Conclusion**:
- From the analysis, the muscles that act involuntarily are:
- (ii) Smooth muscles
- (iii) Cardiac muscles

### Final Answer:
The muscles that act involuntarily are **(ii) Smooth muscles and (iii) Cardiac muscles**.

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