We work with the trees data set that comes with R. (a) Find the type of the trees data object. (b) Produce a figure with two overlaid scatterplots: Height versus Girth, Volume versus Girth(The Girth is on the x-axis). Do the Height plot with blue "+" symbols, and do the Volume plot with red "o" symbols. You need to learn to set the ylim= control option so that all points from the two plots can all show up on the merged figure. Hint: you should use plot() then points() to create the overlaid two scatterplots