HUDSON — And then there were three. The trio of finalists vying to become Hudson's next executive assistant were presented to the Board of Selectmen on Monday, two months ahead of the retirement of incumbent Thomas Moses. Bernie Lynch, principal and founder of Plymouth-based Community Paradigm Associates, which was tasked with helping the town selection committee find Moses' successor, introduced the finalists. They are: Ryan Ferrara, town administrator in Boxborough; Thomas Gregory, town administrator in Spencer and Nina Nazarian, a consultant who has worked as town administrator in Littleton and Princeton. He said after an initial pool of candidates was whittled from 33 to 17, seven applicants underwent a more intensive interview. From that process, the finalists were selected.