毛细血管非常细小，肉眼几乎看不见。

___Capillaries are so tiny that they're almost invisible to the naked eye.

这些毛细血管般的细线在显微镜下几乎看不见。

These ___capillary-thin threads are almost invisible under the microscope.

科学家用毛细管精确测量液体的上升高度。

Scientists use a ___capillary to measure the precise height of liquid rising.