x1<-c(171,175,159,155,152,158,154,164,168,166,159,164)
> x2<-c(57,64,41,38,35,44,41,51,57,49,47,46)
> plot(x1,x2,xlim=c(145,180),ylim=c(25,75))
> lines(c(150,178),c(33,66));text(180,68,"y1")    请问这行里c(150,178),c(33,66)是什么意思？text(180,68,"y1")是什么意思> lines(c(161,168),c(60,38));text(161,63,"y2")    text(161,63,"y2")是什么意思