WASHINGTON — Airport security officers around the nation have been alerted by federal officials to look out for terrorists practicing to carry explosive components onto aircraft, based on four curious seizures at airports since last September. The unclassified alert was distributed on July 20... The seizures at airports in San Diego, Milwaukee, Houston and Baltimore included "wires, switches, pipes or tubes, cell phone components and dense clay-like substances," including block cheese, the bulletin said. "The unusual nature and increase in number of these improvised items raise concern." Security officers were urged to keep an eye out for "ordinary items that...