The Medford Public Library is hosting a 10-week U.S. Citizenship Prep Class directed by the St. Mark Community Education program of Dorchester.  The class will meet from 10 a.m. to noon on Saturdays from April 13 through June 15. To participate you must have had green card for at least 4 years and 6 months, or if married to an American citizen, 2 years and 6 months. To register, go to the St. Mark class registration web page.