gapminder<-read.csv("gapminder.csv",header = T)
library(ggplot2)
p <- ggplot(data = gapminder,
            mapping = aes(
                x = year, 
                y = lifeExp,
                group = country))
p1<-p + geom_line() + 
    facet_wrap(~ continent)
p1
p2.1<- p1+
    geom_hline(yintercept =40,linetype=2)+
    geom_hline(yintercept =60,linetype=2)+
    theme_bw() +
    theme(panel.grid.major = element_blank(), 
          panel.grid.minor = element_blank(),
          axis.text = element_text(size=8, face = "bold"),
          strip.text = element_text(size = 10, face = "bold"))
p2.1
          
p1<-p + geom_line() + 
    geom_point() +
    facet_wrap(~ continent)
p1
p2.2<- p1+
    geom_hline(yintercept =40,linetype=2)+
    geom_hline(yintercept =60,linetype=2)+
    theme_bw() +
    theme(panel.grid.major = element_blank(), 
          panel.grid.minor = element_blank(),
          axis.text = element_text(size=8, face = "bold"),
          strip.text = element_text(size = 10, face = "bold"))
p2.2