Darko达尔科darkadj.黑暗的；深色的n.黑暗；暗处；深色调v.使变黑；变黑Dark-light cycle光暗循环darkish complexion面色苍黑dark-room camera暗室式照相机Dark in complexion黑眉乌嘴Dark clouds massed阴云密布dark-haired woman黑发女人dark-complexioned深肤色的dark room apparatus暗室设备dark pulse spectrum暗脉冲谱dark sky background夜天背景

1. The problem is that dark matter is invisible.
   问题在于暗物质看不见。
2. Hot dark matter consists of particles that travel with relativistic velocities.
   热暗物质由以相对论速度行进的粒子组成。