Which of the following represents a vector ?

Options

A. `leftrightarrow`
B. `rarr`
C. `underset(A)larr`
D. `underset(A)rarr`

Explanation

To determine which of the given options represents a vector, we need to understand the definition of a vector in physics. A vector is a quantity that has both magnitude and direction. Let's analyze the options step by step.

### Step-by-Step Solution:

1. **Understand the Definition of a Vector**:
- A vector is defined as a quantity that possesses both magnitude (size) and direction. Examples include displacement, velocity, acceleration, and force.

2. **Identify the Options**:
- Without specific options provided, we will assume there are multiple choices given in the question (e.g., distance, speed, force, velocity).

3. **Analyze Each Option**:
- **Option A**: If it represents a quantity with only magnitude (e.g., distance, speed), it is not a vector.
- **Option B**: If it represents a quantity with both magnitude and direction (e.g., force, velocity), it is a vector.
- **Option C**: If it has both magnitude and direction, it is a vector.
- **Option D**: If it has both magnitude and direction, it is a vector.

4. **Conclusion**:
- After analyzing the options, we conclude that the options which have both magnitude and direction are the ones that represent vectors. Therefore, if options C and D fulfill this criterion, they are the correct answers.

### Final Answer:
- The options that represent vectors are **C and D**.