Just begining to study latin using D'Ooge.
The sentence in exercise 99 II.2 is
'' My son Sextus is carrying his booty to th Roman camp.''
The answer in the answer key is
'' Filius meus Sextus praedam suam in castra Romana portat. ''
Now, if 'castra Romana' is acc. plural, when prepostion 'in' is used incorrectly, 'cause in goes with ablative (see 53).
In my opinion the translation should go like this:
'' Filius meus Sextus praedam suam ad castra Romana portat. "
Am I right, or have I missed something?