Hi,

Requesting you to please post the full question...we will be glad to answer the same.

I see that this was not from an actual question, but rather from the lesson portion of the Official Guide and that you have posted the entire error and correction, so there is nothing additional that you could have posted.

This particular error is one of "accuracy." This is a relatively rare error in sentence correction compared to something like subject-verb number agreement (singular vs plural).

The error in accuracy is that the original says, "In the Middle Ages, the world was flat." Of course the world was not actually flat but was mistakenly believed to be flat. The corrected version accurately captures the fact that it was a belief that the world was flat, not a fact.

At Veritas, we categorize this lack of accuracy as a secondary error and as such you would save this type of error for last. The page in the Official Guide does not make it very clear, but I would recommend that you use grammar errors as the first way to eliminate incorrect answers and then watch for these secondary errors once you have narrowed the choices down a bit and especially when your remaining choices do not contain any obvious grammar errors.

Hope that helps!

Thank you so much for ur anwer! u made it very clear.