sentences:  By May 2019, Class 710s started to be introduced into service.In late 2007 and early 2008, orders were placed with Bombardier by two rolling-stock leasing companies to purchase a number of Class 172 "Turbostar" trains.In December 2007, Porterbrook ordered 15 three-car and 12 two-car trains for London Midland for delivery in 2010.