题目

--I like British culture very much，and I once went to London. --How long ______ there? A. did you stay            B. have you stayed      C. were you staying        D. had you stayed 答案：A用化学元素符号回答：　　(1)空气中含量最多的气体是____；地壳中含量最多的金属元素是____；　　(2)两个氧原子____；钙原子____.