Explanation:

- Option 1: Science, not rule of thumb

- Focuses on using scientific methods instead of relying on traditional or guesswork methods.

- Aims for efficiency through data and experiments.

- Option 2: Co-operation, not individualism

- Emphasizes teamwork.

- Encourages collaboration between management and workers for mutual benefit.

- Option 3: Harmony, not discord

- Advocates for a peaceful and cooperative work environment.

- Ensures that both employers and employees can achieve prosperity together.

- Focuses on aligning the interests of both management and workers, making it the correct answer for the given statement.

- Option 4: All of the above

- Includes all principles.

- However, doesn't specifically address the unity of interests in the given statement.