Phillip ii's goal was to conquer persia. why did alexander continue his campaign of conquest after this goal had been achieved?

The reason for this was that Alexander was a great general who saw an opportunity which he had to seize. He knew that by making his empire grow very big, it would make him a better general in the eyes of history, it also meant he would be more powerful. However, he didn't consider the original plan of conquering only Persia the most important thing. His eyes have always been set on conquering as much land as possible, especially after he saw in his first victories that his tactics were working great. 

The answer should be a.