выписать придаточные предложения: The early railway builders laid wooden stringers lengthwise, fastening straps of iron on top of the stringers to serve as rails. The practice of laying wooden stringers soon gave way to iron rails which did not prove satisfactory, as they were subject to buckling and warping1 and wore out rapidly. Steel rails were first rolled in England in 1856. From that date they rapidly became the standard type. In England and in the USA rails vary in weight from 50 to 152 pounds per running yard, 2 the average being about 94 pounds per yard. Increasing size of locomotives and trains and greater speed of train movement in both freight and passenger service have made necessary an increasing of rails weights. The standard length of a single rail in America is 39 feet, 60 foot rail is common in Europe. The use of longer rail is advantageous in maintenance work. On modern development in the upkeep of the permanent way is the use of welding process. Most railway travellers are fairly familiar with the crossings or forks of the permanent way where one track diverges from another. These rail crossings wear away fairly rapidly. They are costly to make and also to maintain. In order to reduce the expense in maintaining these joints and crossings, welding processes are now being used, so that new metal can be welded on the worn parts of the crossings in such a way as to build up the rails to their original form