sexual act with a minor."); United States Yang, 128 F.3d 1065, 1072 (7th Ci/.1997); United States 1. Meacham, 115 F.3d 14882.1495 (10th Cir.1997); United States Sirois, 87 F.3d 34, 39 (2d Cir.1996); United States' Campbell, 49 F.3d 1079, 1082-83 (5th Cir.1995) ("[I]t is not necessary to a conviction under the [Mann