What Technique Is Necessary to Produce a Telescope for Focusing

Multiple Choice

What technique is necessary to produce a telescope for focusing X-rays from astronomical sources?

A) The telescope must be placed at high-altitude mountain sites because the X-rays penetrate only this far into the atmosphere.
B) The main mirror must be cooled to prevent the highly energetic X-ray photons from heating and distorting it, thereby producing poor images.
C) The X-rays must be reflected at grazing incidence to the mirror surface; otherwise they will simply pass straight through the mirror.
D) The mirror surface has to have a thick aluminum coating in order to reflect the highly penetrating X-rays.