In the following sequence of reactions a compound A, (molecular formula C$$_6$$H$$_{12}$$O$$_2$$) with a straight chain structure gives a C$$_4$$ carboxylic acid. A is:
$$A \xrightarrow[\mathrm{H_3O^+}]{\mathrm{LiAlH_4}} B \xrightarrow{\text{Oxidation}} \text{C}_4\text{-carboxylic acid}$$

A

B

$$CH_3 - CH_2 - CH_2 - O - CH = CH - CH_2 - OH$$

C

$$CH_3 - CH_2 - CH_2 - COO - CH_2 - CH_3$$

D

$$CH_3 - CH_2 - COO - CH_2 - CH_2 - CH_3$$