通常状况下,X、Y和Z是三种气态单质。X的组成元素是第三周期原子半径最小的元素(稀有气体元素除外);Y和Z均由元素R组成,反应Y+2I-+2H+ I2+Z+H2O常作为Y的鉴定反应。 ⑴Y与Z的关系是(选填字母) 。 a.同位素 b.同系物 c.同素异形体 d.同分异构体 ⑵将Y和二氧化硫分别通入品红溶液,都能使品红褪色。简述用褪色的溶液区别二者的实验方法 ―Did you attend your son's graduation ceremony yesterday?― I______, but I had to go to an important meeting. A.used to B.ought to C.must have D.should have