Which of the following is not a property of a parallelogram?

Options

A. The opposite sides are parallel
B. The consecutive angles are supplementary.
C. The two diagonals bisect at right angles.
D. none of these

Answer

To determine which of the following is not a property of a parallelogram, we first need to understand the properties of a parallelogram.

### Step-by-Step Solution:

1. **Identify the Properties of a Parallelogram**:
- Opposite sides are equal in length.
- Opposite angles are equal.
- Consecutive angles are supplementary (i.e., they add up to 180 degrees).
- The diagonals bisect each other.

2. **List the Given Options**:
- Let's assume the options provided are:
1. Opposite sides are equal.
2. Opposite angles are equal.
3. Consecutive angles are supplementary.
4. The diagonals bisect each other at right angles.

3. **Analyze Each Option**:
- **Option 1**: Opposite sides are equal. (This is a property of a parallelogram.)
- **Option 2**: Opposite angles are equal. (This is also a property of a parallelogram.)
- **Option 3**: Consecutive angles are supplementary. (This is a property of a parallelogram.)
- **Option 4**: The diagonals bisect each other at right angles. (This is not a property of all parallelograms; it is true for rectangles and squares but not for all parallelograms.)

4. **Conclusion**:
- The option that is not a property of a parallelogram is **Option 4**: The diagonals bisect each other at right angles.

### Final Answer:
The option that is not a property of a parallelogram is **Option 4**.