Fill in the blanks.
a. The angle through which an object turns before it looks exactly as it looked before the rotation started is called ___________.

Options

A. Axis
B. angle of rotation
C. line of symmetry
D. none of these

Answer

To solve the fill-in-the-blank question, we need to identify the term that describes the angle through which an object turns before it looks exactly as it did before the rotation started.

### Step-by-Step Solution:

1. **Understanding the Concept**:
- When an object is rotated, it can turn around a point or axis. We need to find out what this specific angle is called when the object appears the same as it did before the rotation.

2. **Identifying the Object**:
- Consider a shape like a square. If we rotate it by certain angles, it may look the same at specific intervals.

3. **Example of Rotation**:
- For instance, if we rotate a square by 90 degrees, it still looks like a square. This is because a square has rotational symmetry.

4. **Finding the Term**:
- The angle through which the object must be turned to look the same as it did before is referred to as the "angle of rotation".

5. **Conclusion**:
- Therefore, the answer to the fill-in-the-blank question is: "The angle through which an object turns before it looks exactly as it looked before the rotation started is called **angle of rotation**."

### Final Answer:
The angle through which an object turns before it looks exactly as it looked before the rotation started is called **angle of rotation**.