题目

 Right now nobody or no group has admitted the ________ for the bus attacks which killed ten and injured a hundred more. A. similarity                   B. devotion                 C. responsibility         D. mystery 答案：A工业用盐(主要成分是NaNO2)外观与NaCl极为相似，但工业用盐有毒，分析NaNO2中氮元素的化合价为A．+1B．+2C．+3D．+5