South Korea was in mourning Monday as investigators worked to determine the cause of a plane crash in Muan that killed 179 of the 181 people on board. Acting President Choi Sang-mok appeared Monday at a memorial in Muan, about 290 kilometers south of Seoul, where he laid a flower and bowed in respect to the victims. A senior official at South Korea’s Ministry of Land, Infrastructure and Transport told reporters that officials planned to conduct a special investigation of all the Boeing 737-800 planes operating in the country. The crashed plane’s flight data recorder will be sent to a