If colleges and universities can hire a large number of graduates from first-class universities overseas, it will undoubtedly help to improve the quality of teaching and scientific research. Therefore, the employment of graduates who have obtained doctoral degrees from domestic universities will not help improve the quality of teaching and research. Which of the following ____ items, if true, will constitute the most powerful questioning of the above views. ['Higher education institutions cannot fully recruit graduates who have obtained PhD degrees from top overseas universities.', 'In many colleges and universities, a considerable number of teachers have graduated from domestic colleges and have no experience of studying abroad.', 'Graduates who have obtained a PhD from top overseas universities are more willing to stay overseas for employment, even after returning to China, they tend to work in foreign companies.', 'Graduates hired by higher education institutions to obtain doctoral degrees from top overseas universities are usually jointly trained by domestic universities and overseas universities, and they also have doctoral certificates issued by domestic universities.']