Strongly acidic aqueous solutions

Question

You have two neutral solutions. One contains the indicator methyl red, which turns red in strongly acidic aqueous solutions but is otherwise yellow. The other contains the indicator phenol red, which turns red in strongly basic aqueous solutions but is otherwise yellow. Which of these steps would cause a color change in both solutions?

1. Add a weak acid to both solutions.
2. Add a strong acid to both solutions.
3. Add a strong acid to one solution, and a strong base to the other.
4. Add a weak acid to one solution, and a weak base to the other.