Consider a schema with two relations, R$1($A$,$B$)$ and R$2($B$,$C$),$ where all values are

integers. Three of the four expressions below produce the same answer. Choose the

expression that produces a different answer:

a$)\backslash$Pi A$,$ B $($R$1$ R$2)$

b$)$ R$1\backslash$Pi B $($R$2)$

c$)$ R$1\backslash$cap $(\backslash$Pi A $($R$1)$ X $\backslash$Pi B$($R$2))$

d$)\backslash$Pi A$,$ R$1.$B$($R$1$ X R$2)$