【正文】 Brain D． A New Machine to Help the Brain Passage 2 Swimming the English Channel requires a tremendous amount of courage and strength， as well as careful training and planning． The three main problems that a swimmer faces are the coldness of the wa ter， the strong tides， and the roughness of the waves in the channel． Even in swimmer the temperature of the water is never warmer than 50 to 68 degrees， which is the reason most swimmers make their attempts in August when the water is usually warmest． The main difficulty in training for channel swimming is being accustomed to the cold． Swimmers usually spend three to four months practicing in the channel，gradually lengthening the time each day un til they can stay in the cold water ten or fifteen hours art a stretch in the last stages of training． As added protection against the cold， be fore they begin a channel crossing， the swimmers cover themselves with a layer of heavy， brownish axle grease， putting on coating 1／ 1 6 to 1／ 8 inch thick． Much of the success in swimming the channel depends upon the timing with the tides． The direct distance from Cap Gris Nez in France to Dover． England— across the narrowest part of the channel— is 2l miles， but the swimmer must go a much longer distance because he does not travel in a straight line in order to swim with the tide chan ges． Perfect planning and timing are necessary to avoid being caught by the turn of the tide just as he nears the other side． Boats equipped with radar now follow channel swimmers and help keep them on course with the tide changes． Channel swimmers must face the swift currents that move in thechannel． Oflen a swimmer will e within a mile of the shore whenthe tide changes， making it difficult or impossible to finish the event． Some swimmers are swept SO far off course that the swim from 30 to. 45 miles in the process． Rough waves are also difficult to battle； channel waters are relatively smooth for only a few days each month， and even then there are likely to be dangerous cross cutxent and sudden weather changes． 6． In the passage， the answers Call be found to all the tbllowing questions EXCEPT ________________ . A． How does a swimmer get ready for a crossing? B． Why is timing SO important to a channel swimmer? C． How far should a swimmer swim in crossing the channel? D． What risks does a swimmer run in crossing the channel? 7． The main aim in training for channel swimming is __________ . A． to be used to the water temperature in August B． to learn to lengthen the practicing time each day C． to be accustomed to being covered with grease as a protection D． to be good at standing the long hours in cold water 8． A successful channel swimmer iS said to be the swimmer who _________