题目

Tokyo 2020 Olympic organizers are encouraging people living in Japan to help make the medals for the games by donating(捐赠)their useless smart phones for recycling.It will avoid waste and benefit the environment.The organizing committee says that it has cooperated with NTT Docomo,a telecommunications giant in Japan,and hopes to collect up to 8 tons of metal from useless electronic devices(设备).“Tokyo 2020 Olympic medals will be made in order to avoid waste,”said three-time Olympic gold medal-winning gymnast Kohei Uchimura.“I think thereis an important message in this for future gen今有60℃CuSO4饱和溶液210 g，加热蒸发掉50 g水后，再降至20℃，可析出CuSO4·5H2O晶体的质量为(　   )（溶解度60℃为40 g，20℃为20 g） 　　A．40 g 　　B．20 g 　　C．70 g 　　D．80 g