Smooth muscle fibres are

Options

A. spindle-shaped, unbranched, non-striated, multinucleate and involuntary
B. spindle-shaped, unbranched, unstriated, uninucleate and involuntary
C. cylindrical, striated, unbranched, multi nucleate and voluntary
D. cylindrical, unbranched, non-striated, multinucleate and involuntary.

Explanation

To answer the question "Smooth muscle fibres are," we need to analyze the characteristics of smooth muscle fibers based on the options provided. Here’s a step-by-step breakdown:

### Step 1: Understand the Characteristics of Smooth Muscle Fibers
- Smooth muscle fibers are a type of involuntary muscle found in various internal organs.
- They are not under conscious control, meaning their movements are involuntary.
- They do not have striations (bands), which distinguishes them from skeletal muscle.
- The shape of smooth muscle fibers is spindle-shaped (tapered at both ends).
- They are unbranched, meaning they do not form branches like cardiac muscle fibers.
- Smooth muscle fibers are uninucleated, meaning each fiber has a single nucleus.

### Step 2: Analyze Each Option
- **Option A**: Spindle shaped, unbranched, non-striated, multinucleated, and involuntary.
- Incorrect because smooth muscle fibers are uninucleated, not multinucleated.

- **Option B**: Spindle shaped, unbranched, unstated, uninucleated, and involuntary.
- Correct as it matches all characteristics of smooth muscle fibers.

- **Option C**: Cylindrical, striated, unbranched, multinucleated, and involuntary.
- Incorrect because smooth muscle fibers are not cylindrical, striated, or multinucleated.

- **Option D**: Cylindrical, unbranched, non-striated, multinucleated, and involuntary.
- Incorrect for the same reasons as option C.

### Step 3: Conclusion
The correct answer is **Option B**: Spindle shaped, unbranched, non-striated, uninucleated, and involuntary.