The sewage treatment in septic tanks is due to__________________?

A. House sewers
B. Lateral sewers
C. Branch sewers
D. Main sewers

A. Bacterias
B. Suspended solids
C. Sediments
D. Hardness

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true