 Complete the following phrase:  Stefan Holtz born 27 February 1981 is a German sprint canoeist who has competed since 2004. He won seven medals at the ICF Canoe Sprint World Championships with two golds C-2 500 m: 2009, C-4 1000 m: 2006, three silvers C-2 500 m: 2006, C-4 500 m: 2007, C-4 1000 m: 2007, and two bronzes C-2 200 m: 2009, C-4 1000 m: 