$E_{11}\left (\underline AB \right )$ and $E_{12}\left (\underline {AC} \right )$ is obvious separation but can we not merge like this to satisfy 2NF $E_{11}R\left (\underline ABD \right )$
As $A$ is a primary key, apart from $A\rightarrow B$, $A\rightarrow D$ also satisfies because of full participation. What are the actual tables?