Singers and audience members are invited to a free "Sing-Along Messiah" concert Sunday, December 11, starting 4 p.m. at Bethany Presbyterian Church, 5625-24th Street, Sacramento (off Fruitridge Road between Freeport Boulevard and Highway 99). Ample free parking is available. Choral conductors from area churches and schools will take turns leading the massed volunteer choir, which is expected to consist of more than 100 singers. Participants are encouraged to bring their own Messiah music scores; a limited quantity of Messiah scores will be available for purchase ($10) at the door. "By popular demand, we are repeating last year's very successful event, says Dr. May Tuan Tucker, Bethany Ch