Health Medical Homework Help

I’m working on a health & medical project and need an explanation and answer to help me learn.

I need some sentences in PAST TENSE to use it in background of study. name of my study “use of electronic cigarettes’ in smoking cessation in Saudi Arabia.(studies links in the attachments) 

The sentences about ( prevalence of use E cigarettes world wide , risks of E cigarettes, , then prevalence of E cigarettes in Saudi Arabia , studies about role of E cigarettes in cessation )