Finish the following sentence with the best choice: How to shape an old sawzall blade into a knife blade.

Choices:
- Hold the sawzall blade by the back edge and carefully grind off all the teeth with a belt grinder. Hold the blade at a 20 degree angle and sharpen one side, flip over and sharpen the other side.
- Hold the sawzall blade by the back edge and carefully grind off all the teeth with a belt grinder. Hold the blade at a 90 degree angle and sharpen one side, flip over and sharpen the other side.

Answer:
Hold the sawzall blade by the back edge and carefully grind off all the teeth with a belt grinder. Hold the blade at a 20 degree angle and sharpen one side, flip over and sharpen the other side.