The normal rain water is slightly acidic and its pH value is 5.6 because of which one of the following?

A

$$CO_2 + H_2O \rightarrow H_2CO_3$$

B

$$N_2O_5 + H_2O \rightarrow 2HNO_3$$

C

$$2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4$$

D

$$4NO_2 + O_2 + 2H_2O \rightarrow 4HNO_3$$