Final answer:
The teacher most likely means that Susana's sources were not believable or trustworthy.
Step-by-step explanation:
When the teacher says that Susana's sources were not credible, they most likely mean that her sources were not believable or trustworthy. Credible sources are those that are reliable, accurate, and can be trusted to provide accurate information. Susana's sources might have lacked credibility if they were biased, unsupported by evidence, or came from unreliable or untrustworthy sources.