Question

fed v. anti - federalists
why could the articles not be changed?
the document was too long.
rhode island representatives did not show up and they needed unanimous consent
the document was too short.
there was no need for change.

Explanation:

The Articles of Confederation required unanimous consent from all 13 states to amend the document. Rhode Island often refused to participate in amendment votes, blocking any changes since full agreement could not be reached. The other options are irrelevant to the actual barrier to amending the Articles.

Answer:

Rhode Island representatives did not show up and they needed unanimous consent