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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def start(self):
 """The event's start time, as a timezone-aware datetime object"""

        if self.start_time is None:
            time = datetime.time(hour=19, tzinfo=CET)
        else:
            time = self.start_time.replace(tzinfo=CET)
        return datetime.datetime.combine(self.date, time)