Final answer:
The inability of the Confederation Congress to enforce laws across states weakened the central government, as states could ignore or modify these laws, leading to confusion and instability.
Step-by-step explanation:
The Confederation Congress's inability to enforce laws weakened the central government because states could effectively ignore national legislation. This situation meant the central government lacked the necessary power to maintain unity and enforce consistent policies across the states. The correct answer to the question is D: States could change laws or not apply them equally, causing confusion and lack of stability. This created an environment where states often refused to fund or comply with national policies, especially if those policies conflicted with their own interests, leading to a system that was inefficient and unable to function effectively as a unified nation. The lack of a central authority to raise an army or navy and to directly impose taxes meant that the national government could not independently ensure defense or financial stability, which was highlighted by events such as Shays' Rebellion, where the national government's weaknesses were brought to the fore.