题目

   As space science develops, man has learned more and more about space. Space is not only amazing but also dangerous. While working in space, spacemen are facing danger as well as success.    Scientists have found out that the radiation（辐射） is the greatest danger to spacemen in space. When spacemen are working in space, they are in danger of the radiation from the sun and other stars, which is bad for their health. The harm of the radiation won’t be found until their children even grandchildren are born. Some special medicine may work a little, but no really effective me25个X的和再减去5的差是________．