3.At the 1908 Olympics in London the Marathon race was held on a very hot day.The race started at Windsor Castle,one of the homes of the Royal Family,so that the Royal children could see the runners leave.The race was planned to continue for 26 miles 385 yards (42,195 metres),now the accepted distance for this race,into Central London.Because of the great heat,however,many runners had to give up before they could finish the race.Towards the end,the large crowd waited with great excitement for the South African,Charles Hefferon,to come into the stadium first.They were surprised,however,when the 1st man to appear was the small Italian,Pietri Dorando.Dorando was by now extremely tired and weak and,as he was running round the stadium towards the finishing line,he fell to the groud,unable to continue.Doctors rushed to help him and he soon got to his feet and continued,with loud cheers from the crowd.As he came close to the line he had to be helped again, this time by a journalist,but finally he finished the race.He was not,of course,allowed to receive the gold because he had had help during the race.Afterwards, Dorando argued unsuccessfully that he had not asked for this help.But the medal was given to an American,Hayes,who had finished second.However, Dorando later received a special gold cup from Queen Alexandra for his courage. 问题：the accepted distance for the Marathon race was about ( )

A. 50km

B. 40km

C. 30km

D. 20km