Today, most countries in the world have canals.Many countries have built canals near the coast, and parallel____1____ the coast.Even in the twentieth century, goods can be moved more cheaply by boat than by any other ____2____ of transport. These ____3____ make it possible for boats to travel ____4____ ports along the coast without being ____5____ to the dangers of the open.Some canals, such as the Suez and the Panama, save ships weeks of time by making their ____6____ a thousand miles shorter.Other canals permit boats to reach cities that are not ____7____ on the coast, still other canals ____8____ landsswheresthere is too much water, help to ____9____ fields wherethere is not enough water, and ____10____ water power for factories and mills.The size of a canal ____11____ on the kind of boats going through it.The canal must be wide enough to permit two of the largest boats using it to ____12____ each other easily.It must be deep enough to leave about two feet of water ____13____ the keel of the largest boat using the canal.When the planet Mars was first ____14____ through a telescope, people saw that the round disk of the planet was criss-crossed by a ____15____ of strange blue-green lines.These were calledcanals ____16____ they looked the same as canals on earth ____17____ are viewed from an airplane.However, scientists are now ____18____ that the Martian phenomena are really not canals.The photographs ____19____ from space-ships have helped us to ____20____ the truth about the Martiacanals.
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