I want add the sign (a), (b), (c) to my figures. what I mean is add the (a),(b),(c) to the upper left of the graph
a<-rnorm(1000,10,1)
plot(a)
b<-rnorm(1000,10,10)
plot(b)
c<-rnorm(1000,1,1)
plot(c)
Could anyone tell me how can I add this?
Thank you
like this