Consider a schema with two relations, $R1(A,B)$ and $R2(B,C),$ where all values are

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

expression that produces a different answer:

a$){}_{A,B}(R1|><mi\; id="EditorElement\_4661090">|</mi><mi\; id="EditorElement\_4661092">R</mi><mn\; id="EditorElement\_4661094">2</mn><mi\; id="EditorElement\_4661096">)</mi>$

b$)R1|><mi\; id="EditorElement\_4661021">|</mi><msub\; id="EditorElement\_4661030"><mrow><mi\; id="EditorElement\_4661023"></mi></mrow><mrow\; id="EditorElement\_4661029"><mi\; id="EditorElement\_4661026">B</mi></mrow></msub><mi\; id="EditorElement\_4661036">(</mi><mi\; id="EditorElement\_4661033">R</mi><mn\; id="EditorElement\_4661035">2</mn><mi\; id="EditorElement\_4661037">)</mi>$

c$)$

d$){}_{A,R1.B}(R1R2)$