Contested races are shaping up for some key positions in the annual town election on May 17. Political newcomer Christopher David Cataldo has taken out nomination papers for a three-year seat on the Board of Selectmen. Incumbent Ellen Allan, who chairs the board and is up for reelection, has also taken out nomination papers. There are two seats up for grabs on the School Committee. Incumbent Kiersten Warendorf, the chairwoman, is seeking reelection, but two-term board member Brian Noble is not. In addition to Warendorf, two candidates have taken out nomination papers for the two three-year seats on the committee: Erin Reardon and Alison Link. Incumbent Town Clerk Patricia Anderson has taken out — and returned — nomination papers for the job she has held since 2008, and Jill O’Loughlin also has taken out nomination papers for that job. The last day to obtain nomination papers is March 27, and they must be returned with the signatures of at least 52 registered voters by 5 p.m. on March 31.