With regards to the expressive power of the formal relational query languages, which of the following statements is true?
Relational algebra has the same power as safe relational calculus as:
Option "B" is also correct but option "C" is more appropriate because Relational calculus have some unsafe operations and because of those unsafe operations sometimes it may fall in ∞(infinite) loop.
so relational algebra has the same power as safe relational calculus
A bit more specific guide for GO can be found...