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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 add_answer_at_time(self, record, now):
 """Adds an answer if if does not expire by a certain time"""

        if record is not None:
            if now == 0 or not record.is_expired(now):
                self.answers.append((record, now))
                if record.rrsig is not None:
                    self.answers.append((record.rrsig, now))