Step 1: Form alcohol B.
The alkyl bromide $C_4H_9Br$ reacts with NaOH and the OH replaces Br: $RBr+NaOH\rightarrow ROH$. So B is a primary alcohol.
Step 2: Decide the oxidation needed.
To go all the way to a carboxylic acid D, we need a strong oxidising agent. A mild agent would stop at the aldehyde.
Step 3: Reject PCC.
PCC is mild and stops oxidation at the aldehyde stage, so it cannot make the acid.
Step 4: Reject Tollens and cold dilute KMnO4.
Tollens reagent and cold dilute permanganate are not the standard full oxidisers used here for converting a primary alcohol straight to the acid.
Step 5: Choose CrO3-H2SO4.
Jones reagent $CrO_3$ in $H_2SO_4$ is a strong oxidiser that takes a primary alcohol fully to a carboxylic acid. So $C=CrO_3-H_2SO_4$.
Step 6: State the answer.
\[ \boxed{C=CrO_3\text{-}H_2SO_4,\ D=\text{carboxylic acid}} \]