Nitrobenzene undergoes catalytic hydrogenation in the presence of (H_2/Pd) to reduce the nitro group (({-}NO_2)) into a primary amino group (({-}NH_2)).

Thus,

$$C_6H_5NO_2\xrightarrow{H_2/Pd,\ C_2H_5OH}C_6H_5NH_2.$$

Hence,

$$\boxed{[A]=\text{Aniline }(C_6H_5NH_2).}$$

Aniline then reacts with acetic anhydride in the presence of pyridine to undergo acetylation, forming the corresponding amide, acetanilide.

The reaction is

$$C_6H_5NH_2+(CH_3CO)_2O\xrightarrow{\text{Pyridine}}C_6H_5NHCOCH_3+CH_3COOH.$$

Hence,

$$\boxed{[B]=\text{Acetanilide }(C_6H_5NHCOCH_3).}$$

Therefore,

$$\boxed{[A]=\text{Aniline},\qquad [B]=\text{Acetanilide}.}$$