Acid rain pH lowers because of—

1. $\mathrm{CO_2}$ from vehicles, power plants and industries
2. $\mathrm{SO_2}$ and $\mathrm{NO_x}$ from coal/petroleum-burning power plants and brick kilns
3. dissolved $\mathrm{H_2}$ from rivers

• ai and ii
• bii and iii
• ci and iii
• di, ii and iii