Reduction thinking refers to when the problem is difficult to solve directly, according to the nature of the problem, the conditions and the characteristics of the relationship; the appropriate transformation method is used to convert the problem, and finally it is reduced to an easy, simpler or solved problem thought of. Based on the above definitions, Which of the following uses the idea of reduction:. ['Mankind invented the electric bulb using tungsten wire as the filament, which replaced the conventional carbon wire electric lamp, thereby significantly improving the brightness of the electric lamp.', 'After mastering the formulas for calculating the area of the fan and triangle, use the method of graphic segmentation to find the area of the bow.', 'Professor Zhang replaced the previous experimental method with a new experimental method, thereby overcoming a technical problem.', 'Legal researchers have theorized the methodology of law, which has evolved into a methodology of law.']