A white solid A reacts with dilute H2SO4 to produce a colourless gas B and a colourless solution C. The reaction between B and acidified dichromate yields a green solution and a slightly coloured precipitate D. The substance D, when burnt in air, gives a gas E which reacts with B to yield D and a colourless liquid. Anhydrous copper sulphate turns blue with this colourless liquid. The addition of aqueous NH3 or NaOH to C produces a precipitate that dissolves in an excess of the reagent to form a clear solution.
Which of the following gases are B and E respectively?
a. CO2 and SO2
b. SO2 and H2S
c. H2S and SO2
d. CO2 and H2S