Many private institutions of higher education around the country are in er. Not all will be saved, and perhaps not all deserve to be saved. There are low-quality Schools just as there are low-quality businesses. We have no obligation to save them simply because they exist. But many thriving institutions that deserve to continue are threatened. They are doing a fine job educationally, but they are caught in a financial difficulty, with no way to reduce rising costs or increase revenues (收入) significantly. Raising fees doesn’t bring in more revenue, for each time fees go up, the enrollment (注册人数) goes down, or the amount that must be given away in student aid goes up. (78) Schools are bad businesses, whether public or private, not usually because of bad management but because of the nature of the business. They lose money on every customer, and they can go bankrupt either from too few students or too many students. Even a very good college is a very bad business. It is such colleges, thriving but threatened, that I worry about. Low enrollment is not their chief problem. Even with full enrollments, they may go under Efforts to save them, and preferably to keep them private, are a national necessity. (79) There is no basis for arguing that private schools are bound to be better than public schools. There are plentiful examples to the contrary. Anyone can name state universities and colleges that rank as the finest in the nation and the world. it is now inevitable that public institutions will be dominant, and therefore diversity (多样性) is a national necessity. Diversity in the way we support schools tends to give us a healthy diversity in the forms of education. In an imperfect society such as ours, uniformity of education throughout the nation could be erous. In an imperfect society, diversity is a positive good. Eager supporters of public higher education know the importance of keeping private higher education healthy. In the passage, the author asks the public to support______.