单选题 .  The view over a valley of a tiny village with thatched (草盖的)  roof cottages around a church; a driver through a narrow village street lined with thatched cottages painted pink or white; the sight over the rolling hills of a pretty collection of thatched farm buildings—these are still common sights in parts of England. Most people will agree that the thatched roof is an essential part of the attraction of the English countryside.
    Thatching is in fact the oldest of all the building crafts practised in the British Isles. Although thatch has always been used for cottage and farm buildings, it was once used for castles and churches, too.
    Thatching is a solitary craft, which often runs in families. The craft of thatching as it is practiced today has changed very little since the Middle Ages. Over 800 full-time thatchers are employed in England and Wales today, maintaining and renewing the old roofs as well as thatching newer houses. Many property owners choose thatch not only for its beauty but because they know it will keep them cool in summer and warm in winter.
    In fact, if we look at developing countries, over half the world lives under thatch, but they all do it different ways. People in developing countries are often reluctant to go back to traditional materials and would prefer modern buildings. However, they may lack the money to allow them to import the necessary materials. Their temporary mud huts with thatched roofs of wild grasses often only last six months. Thatch which has been done the British way lasts from twenty to sixty years, and is an effective defense against the heat.1.   Which of the following remains a unique feature of the English countryside? ______