Wanderers in that happy valley through two luminous windows saw figures moving musically to a lute's well-tun´d law

what is the most likely explanation for what law means in this line?

a. beat or structure
b. limit or restriction
c. vigor or enthusiasm
d. volume or intensity

The most likely explanation for what law means in this line would be limit or restriction.

The poem "The Haunted Palace" is a ballad — a poem or song that tells a story, often one of tragedy. In the ballad, the haunted house represents the exact thing that the house of Usher does: an ancestral home and name fallen into mental and physical decline.

In a library book about famous wagon trains and the people who ran them

Explanation:

It showed the answer at the end for me, it's this one. The first answer on top is wrong.