page1: 2 issues: add a reference and use data to

page1: 2 issues: add a reference and use data to prove the strong relationship 

page 2: add a reference for the highlighted 3 lines only. 

page4: add the framework

page 7: fix the missing words

page 9: write one page not more than one page about the significance of the study and follow the checklist

page 9: add key terms

page 10: add summary for chapter 1