要延长烘焙食品之保存期间，要靠（）
A.加防腐剂
B.适当包装
C.注意保存条件
D.以上即是
参考答案：D
– Were you at school when I called you?
– Yes, I ________ in the library.
A. studied B. am studying C. was studying
从逻辑结构看，线性表是典型的 【1】 ，树是典型的 【2】 。
