Constructors and local Lao residents attend the drilling-through ceremony of Boten Tunnel along the China-Laos railway in Boten of Laos, March 21, 2019. A Chinese railway engineering company on Thursday drilled through Boten Tunnel, the first major tunnel over 5,000 meters along the China-Laos railway. This marks an important milestone in the construction of the project. The Boten Tunnel, with a length of 6453.5 meters, is among the 10 major tunnels longer than five km along the China-Laos Railway. The tunnel has to pass through unfavorable geology such as karst, bedding rock, fault fracture zone, gypsum, carbon mudstone, and water inrush, and it varies, thus creating lots of difficulties to the Chinese engineering company, China Railway No. 5 Engineering Group (CREC-5). (Xinhua/Wang Jingqiang)