Q: Fact 1: The emission of sulfur dioxide causes acid rain. Fact 2: It's sulfur dioxide (SO2). Given the two facts above, the emission of what causes acid rain?

OPTIONS: [I] H2O; [II] smoke from food; [III] Hydrogen; [IV] coal; [V] SO2; [VI] oil; [VII] CFCs; [VIII] Cars;
The answer is:
[V]