The correct answer is D) though others had published ". . . undertook a new series of measurements. . ."
Many persons likewise published measurements and formulas; but the results were so discordant that Professor Langley undertook a new series of measurements, "Experiments in Aerodynamics. The context clue that gives you the idea that discordant is defined as: "though others had published ". . . undertook a new series of measurements. . ."
This is correct because when there is discordance among the ideas of many people, the result is that they undertake a new series of measurements. That is why the scientific method is considered valid. Because the experiment has to have the same results over and over again And to reach this moment, researchers and scientists have to do many tests using variables until they can get the same result.