Two out of 10 South Korean secondary school students have an experience of drinking alcohol, with 10 percent having also smoked tobacco, a survey showed Monday.    In the education ministry\'s poll of 75,643 elementary and high school students nationwide, 20.6 percent said they have drunk more than one glass of alcohol over the past month. Nearly half of the students who drink were classified as belonging to a \"high-risk\" group, with male students drinking more than five shots of soju, a popular Korean liquor, at one time and female students drinking more than three shots of soju.    The ratio of high-risk drinking students stood at 44.6 percent in 2008 and 47.2 percent in 2010, according to former surveys.    Asked about their smoking habits, 6.1 percent of secondary school students said they smoked almost every day -- 9.1 percent of boys and 2.8 percent of girls. Some 2.8 percent said they smoked more than 10 cigarettes a day.    \"A separate survey in 2010 showed students here first experience smoking at an average age of 12.7 and drinking at 12.8,\" said a lawmaker who obtained survey results from the ministry. \"The government needs to strive to prevent students from smoking and drinking to promote their health and to create sound school environments.\"    In April, the government teamed up with discount retailers, convenience stores and other small vendors nationwide to strictly observe a ban on sales of alcohol and tobacco products to youths under 19, to root out underage smoking and drinking.    A survey conducted by the Center for Disease Control in 2011 indicated 15.8 percent of underage minors attempted to purchase alcohol. Of that number, 6.1 percent said they easily bought alcohol. Cigarettes remain cheap in South Korea, with a pack often costing around 2,500 won (US$2.24).