题目

 42. Little _____ about his own health though he was very ill.  A. he cared           B. did he care    C. he cares         D. does he care 答案：B用相应的化学符号和数字填空：①氢气________； ②氢氧根离子________；③正二价的钙元素________；④2个铁原子________．