吉芬物品是指某种生活必需品,在某种特定条件下,消费者对这种商品的需求与价格成同方向变化。( )
参考答案:对
It's high time you had your hair cut; it's getting ________. [ ]
A.too much long
B.much too long
C.long too much
D.too long much
在数据文件的包含主码的属性集上建立的索引称为()。
A.聚集索引
B.主索引
C.稠密索引
D.辅索引