The four grades of density are shown in these mammogram images.
图中展示了这四个密度等级。
2
The storage density of a disk medium; storing four times the amount of information per disk as single density.
磁盘介质的存储密度，在这种密度下磁盘的信息存储量是单密度盘的四倍。
3
Figures released by the Office for National Statistics show that population density in England is already almost double that of Germany and four times the figure for France.