A body with constant acceleration always moves along a straight line.
A body with constant magnitude of acceleration may not speed up.

Options

A. Statement (I) is true, Statement (II) is true , statement (II) is the correct explanation for Statement (I).
B. Statement (I) is true, Statement (II) is true , statement (II) is not the correct explanation for Statement (I).
C. Statement (I) is true, Statement (II) is false.
D. Statement (i) is false, Statement (II) is true.

Explanation

To solve the question, we need to analyze both statements regarding motion with constant acceleration.

### Step-by-Step Solution:

1. **Understanding the First Statement:**
- The first statement claims that "A body with constant acceleration always moves along a straight line."
- To evaluate this, we need to understand what constant acceleration means. Constant acceleration implies that the acceleration vector does not change in magnitude or direction.
- However, it is important to note that the direction of acceleration can be at an angle to the velocity vector. For example, in projectile motion, the acceleration due to gravity is constant and directed downward, while the object moves in a curved path.
- Therefore, a body can have constant acceleration and still not move in a straight line. This makes the first statement **false**.

2. **Understanding the Second Statement:**
- The second statement claims that "A body with constant magnitude of acceleration may not speed up."
- Here, we need to consider scenarios where the magnitude of acceleration is constant but the direction changes. A prime example of this is uniform circular motion.
- In uniform circular motion, an object moves in a circular path with constant speed. Although the speed remains constant, the direction of the velocity vector changes continuously due to the constant centripetal acceleration directed towards the center of the circle.
- Since the speed does not increase, the second statement is **true**.

3. **Conclusion:**
- Based on the analysis:
- The first statement is false.
- The second statement is true.
- Therefore, the correct answer is that the first statement is false and the second statement is true.

### Final Answer:
- Statement 1: False
- Statement 2: True