What does the multiple-meaning word spell mean in these lines from Robert Frost's "Mending Wall," which describe the task of stacking fallen stones to repair the wall?
And some are loaves and some so nearly balls
We have to use a spell to make them balance . . .
a.magic words spoken to make something happen
b.unbroken or long period of time
c.to order letters correctly to make a word
d.to give someone a break from work so they can rest