Traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds respectively. If they all changed simultaneously at 8:00:00 a.m., at what time will they next change together?
a) 8:06:00a.m.
b) 8:07:12a.m.
c) 8:03:36a.m.
d) 8:07:32a.m.