A school recently conducted a survey on the role of scholarships in promoting learning efficiency, and the results showed that students who received scholarships were, on average, 25% more effective than those who did not receive scholarships. This fully shows that scholarships help students improve The effect of learning efficiency is clear. Which of the following? If true, the above argument can be weakened most. ['Scholarships are usually obtained because those students have good study habits and high learning efficiency.', 'Scholarship students can more easily improve the learning environment to improve learning efficiency.', 'Students with low learning efficiency usually study long and lack normal rest.', 'Research on the level of learning efficiency and the amount of scholarships should be carried out using quantitative methods.']