MEXICO CITY - When Mexican seventh-graders crack open their new biology books this week, they're in for a titillating surprise: Chapter four is all about sex. And it's not the sterilized sex education of the past. For the first time, the federally mandated textbooks broach the once-taboo topics of masturbation and homosexuality while instructing students that there is nothing wrong with either. Church officials and conservative groups are outraged. They charge that the texts — which are required teaching — encourage promiscuity and "abnormal" sexual practices. They are pressuring the federal government to remove passages they consider offensive. "These days,"...