考查名词辨析。A选项fence“栅栏,围墙”;B选项barrier“障碍物,屏障”,可指抽象的“阻力;障碍”,也可以指具体的“障碍物,屏障,关卡,分界线”。例句:The crowd had to stand behind barriers.(人群只好站在障碍物后面。)C选项prevention“预防,阻止,妨碍”,例句:Prevention of a problem is always preferable to trying to cure it.(防止出现问题总是比试图解决问题更可取。)D选项jam“拥挤,困境”,多指交通的堵塞。例句:The bus was delayed in a five-mile jam.(公共汽车因长达五英里的交通堵塞而延误。)句意:对于搬迁异地的人来说,沙漠和高山总是障碍。由选项意思和句意可知,B选项符合句意。