COLUMBIA -- Kiah Seymour, a senior from Archbishop Carroll High School in Washington, D.C., set a new U.S. no. 1 mark in the high school girl’s 400-meter hurdles Saturday, crossing the finish line in 1:01.95 and beating the previous mark of Jennifer Cannon of Tennessee High School of 1:02.60, which she ran last weekend at the Beach Run Invitational in Myrtle Beach.