The completion time of $A$ will be $9$ Unit.
Hence, option (D) is correct.
Here, is the sequence (Consider each block takes one time unit)
$$\begin{array}{|c|c|c|} \hline \textbf {A} &\textbf {B} & \textbf {C} & \textbf{D }& \textbf{A}& \textbf{C}& \textbf{A}& \textbf{C}& \textbf{A} \\\hline \end{array}$$
Completion time of $A$ will be $9$.