Assertion (A): Sulphur dioxide emitted from a coal fired plant can cause acid rain at places hundreds of kilometres away. Reason (R): $\mathrm{SO}{}_2$ is oxidised to $\mathrm{SO}{}_3$ only slowly in air, with particulates and ozone catalysing the oxidation, so much of the conversion to $\mathrm{H}{}_2\mathrm{SO}{}_4$ takes place during transport downwind.

1. ABoth A and R are true and R is the correct explanation of A
2. BBoth A and R are true but R is not the correct explanation of A
3. CA is true but R is false
4. DA is false but R is true