I am no expert, so my opinion is just personal.
However, I think the key is right for No.1. Obviously the clause is led by quae, which indicates the thing it refers is in feminine plural, which should be "artium".
Therefore, the whole sentence should be like this:
The power of arts is also powerful, which (arts) always nourish us.
Your explanation cannot hold, since if so, the "quae" has to be in accusative case, which can only be accusative neutral plural. However, nothing in the main clause is neutral plural. What's more important, is that alunt should be 3rd person plural, which does not agree with the subject nos.
Hope you will find my explanation useful.
Last edited by zhongv1979
on Thu Jan 26, 2006 2:02 pm, edited 1 time in total.