尝试在R上运行我的代码时，它将运行并产生一半的工作。 lines命令没有添加所需的第二行，我也不明白为什么。感谢您的帮助！ 代码：
Forceps <- c(6.61, 4.87, 3.23, 2.00, 1.29, 0.98)
Vacuum <- c(5.05, 7.21, 7.66, 5.93, 5.45, 4.40)
year <- c(1990, 1994, 1998, 2002, 2006, 2010)
plot(year, Forceps, type = "l", xlab = "Year", ylab = "Frequency", main = "Forceps (black) vs Vacuum (red) ", ylim = c(0,10))
lines(year, Vacuum, col = "red”)