High-speed rail (HSR) is a form of railway transportation which runs at a high speed. It uses an integrated system of dedicated tracks and rolling stock to attain the high speed. While there is no single standard that applies worldwide, new lines in excess of 250 kilometers per hour (160 miles per hour) and existing lines in excess of 200 kilometers per hour (120 miles per hour) are widely considered to be high ＿＿（21）＿＿ . The first high-speed train began its ＿＿（22）＿＿ in 1964 in Japan, and they were called bullet trains. They run on standard gauge rail with continuously welded rails. China's HSR (High-speed rail) is the longest HSR network in the world; it is China's network of passenger-dedicated railway. It was extended to 29 more provincial-level administrative divisions in 2017 which gives it a total length of 25,000 km. This ＿＿（23）＿＿ approximately two-thirds of the global high-speed railway for commercial services. In 2017 it completed nearly 2 billion trips. ＿＿（24）＿＿ China has over two-thirds of the World's High-speed rail, its network does not cross into the neighboring nations. The HSR crosses 25 boundaries only in Europe. Belgium is served by four operators TGV, ICE, Eurostar and Thalys trains all from neighboring countries. ICE trains reach Switzerland and Belgium while TGV rail has extended to Italy, Luxembourg, Germany, and Switzerland. Eurostar connects London to Brussels.