L and M belong to two different homologous series. The first three compounds in homologous series L all decolourise aqueous bromine. The first three compounds in homologous series M all dissolve in water and form solutions with a pH below 7. What are the general formulae of homologous series L and M?
- AL: $C_nH_{2n}$; M: $C_nH_{2n+1}COOH$
- BL: $C_nH_{2n}$; M: $C_nH_{2n+1}OH$
- CL: $C_nH_{2n+2}$; M: $C_nH_{2n+1}OH$
- DL: $C_nH_{2n+2}$; M: $C_nH_{2n+1}COOH$