其实，物理学家对暗物质的存在确信无疑，最早上世纪30年代做的天文观察就显示出要保持时刻运转的星系稳定聚集在一起远非一般性物质所能；换句话说，一个星系的可见部分一定是牢牢嵌在一种不可见的光晕上的；否则，它就会在运转过程中四分五散。
Physicists are pretty confident dark matter exists. Astronomical observations first made in the 1930s show there is not nearly enough ordinary matter to hold galaxies together as they spin round.
屏幕上所显示的是 CCNA01# ；对于许多设备来说，这是非常典型的，这个提示符实际上嵌入了一些不可见的控制字符。
What shows on the screen is just CCNA01# ; as is typical for many devices, though, this prompt actually embeds invisible control characters.
线宽太小会导致线条完全不可见，太大则会导致显示没有用的输出，因为线条覆盖了所有的几何图形。
Choosing a line width that is too small results in the lines not being visible at all, and a line width too large renders the output useless because the lines cover all geometries.
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