Paolo Carbonara: Subject-Verb Agreement

An organ grinder named Paolo Carbonara is searching for his monkey. It turns out the monkey walked out because he could not stand the sign on Paolo's back: ""A gift of dollar bills are greatly welcome."" Henry and Miss Newton convince Paolo to change the sign to ""A gift of dollar bills [b]is[/b] greatly welcome."" It's just what Paolo needs to win back the monkey's favor.