With regard to the expressive power of the formal relational

With regard to the expressive power of the formal relational query languages, which of the following statements is true?

1. Relational algebra is more powerful than relational calculus
2. Relational algebra has the same power as relational calculus
3. Relational algebra has the same power as safe relational calculus
4. None of the above

This is a rule of database theory that relational algebra has same power as safe relational calculus.