Even through ordinary transparent materials such as glass or water, the speed of light is slightly reduced because light interacts with the atoms that make up the material. But in this case, the impact is weak and any attempt to strengthen it will Leads to the absorption of light. Therefore, it is important to reduce the speed of light and not to be absorbed. Welchbo soil does this through a cell. This method puts the plutonium atom in a very delicate quantum state In this state, the plutonium atom cannot absorb light. At the same time, the interaction of the two beams of light produces another beam of light with a long wavelength, which travels much slower than the original two beams of light. Which of the following items that is not part of the experiments performed by Welch:. ['Reduce the speed of light without being absorbed.', 'Put thallium atoms in a delicate quantum state that will not absorb light.', 'Make cheap, efficient light sources to avoid being absorbed.', 'Two light beams with slightly different wavelengths interact to produce slow light.']