Today, most countries in the world have canals. Many countries have built canals near the coast, and parallel 【26】______ the coast. Even in the twentieth century, goods can be moved more cheaply by boat than by any other 【27】______ of transport. These 【28】______ make it possible for boats to travel 【29】______ ports along the coast without being 【30】______ to the dangers of the open. Some canals, such as the Suez and the Panama, save ships weeks of time by making their 【31】______ a thousand miles shorter. Other canals permit boats to reach cities that are not 【32】______ on the coast, still other canals 【33】______ lands where there is too much water, help to 【34】______ fields where there is not enough water, and 【35】______ water power for factories and mills. The size of a canal 【36】______ on the kind of boats going through it. The canal must be wide enough to permit two of the largest boats using it to 【37】______ each other easily. It must be deep enough to leave about two feet of water 【38】______ the keel of the largest boat using the canal. When the planet Mars was first 【39】______ through a telescope, people saw that the round disk of the planet was criss-crossed by a 【40】______ of strange blue-green lines. These were called 'canals' 【41】______ they looked the same as canals on earth 【42】______ are viewed from an airplane. However, scientists are now 【43】______ that the Martian phenomena are really not canals. The photographs 【44】______ from space-ships have helped us to 【45】______ the truth about the Martia 'canals'. 【26】