Final answer:
The people at the Ministry first realized there were intruders because they saw them.
Step-by-step explanation:
The people at the Ministry first realized there were intruders because c) they saw them. In the sentence, the phrase 'they saw them' indicates that the Ministry personnel visually observed the intruders. This suggests that the presence of the intruders was directly witnessed by the people at the Ministry, leading them to realize that there were intruders.