Why might the articles have denied congress the power to levy taxes?

To say that taxation was a sensitive subject in the newly independent nation is an understatement. Taxation without representation (that should be a familiar phrase) was one of the principle reasons for declaring independence from the British, and was seen as a symbol of government overreach and violation of individual liberties. The new confederation of states wanted ultra-limited central government, and the issue taxation would have been a highly contested theme that may have threatened the unity of the new republic. 

They showed the country that integration could be successful.

Its either b or c   i'm leaning towards b though i've heard of them during that time period