The correct answer is A. Coolidge tube.
A Coolidge tube is a type of vacuum tube that is used to produce X-rays. It was invented by William D. Coolidge in 1913. The tube consists of a cathode, an anode, and a filament. The cathode is heated, which causes electrons to be emitted. The electrons are then accelerated towards the anode by a high voltage. When the electrons hit the anode, they produce X-rays.
X-ray tubes are used in a variety of applications, including medical imaging, industrial inspection, and security screening.
Option B, X-ray tube, is a general term for any tube that produces X-rays. It does not refer to a specific type of tube.
Option C, Roentgen, is the name of the German physicist who discovered X-rays in 1895. He did not invent the X-ray tube.
Option D, None of these, is incorrect.