Answer:
The answer is a): it had a second apse on the west end.
Explanation:
The three-aisled basilica for the Monastery of Saint Gall was different from early Christian prototypes because a second apse was placed on the west end of its building structure. Also, the Monastery had two towers that were fitted at the western end, unlike how the towers were usually fitted at the front end (facade) of early Christian monastic structures.