第一段changes -----varies
第二段spending---expenditure on this leaped by 10%,reaching the proportion of 50%
第四段There was a downward trend.It decreased from 28% in 1981 to 22% in 1991.Consequently,it descended to only 5% in 2001.最好连成一句吧 There was a downward trend,which subsided from 28% in 1981 to 22% in 1991,and consequently descended to merely 5% 10 years later
第五段experienced up and down---fluctuated,spending---expense
结尾 时态不大对.按你原来的可以改成 In a word,the most principal segment turned out to be the salaries of teachers,occupying approximately half of the overall expenditure.The fluctuation of spending on other issues,such as insurance and resources,could be witnessed as well.