Training for a marathon requires careful preparation and steady, gradual increases in the length of the runs. ___1___, buy the best-fitting, best-built running shoes you can find. No one can say which brand will work best for you or feel best on your feet, so you have to rely on your experience and on the feel of each pair as you shop. When you have found shoes that seem right, walk in them for a few days to double-check the fit. ___2___. As always, you should stretch( 伸展 ) at least ten minutes before each run to prevent injuries.