题目

By high school,T.J.Ware was the most famous troublemaker in his town.Teachers Were afraid to see his name posted on their classroom lists for the next term.He wasn’t Very talkative,didn’t answer questions and got into lots of fights. In a weekend activity all the students at school had been invited to sign up sign up For ACE training,a program designed to have students become more active in their communities.T.J.was one of 405 students who signed up. At the start of the activity,T.J.didn’t readily join the discussion groups and he didn’t seem to have much to say.But slowly,the 质量为250克的物体静止在水中，有一半体积露出水面，这个物体的体积是________米3，它的密度是________千克/米3．