The data frame sorption (DAAG) includes columns ct (concentration–time sum), Cultivar (apple cultivar), Dose (injected dose of methyl bromide), and rep (replicate number, within Cultivar and year)....

The data frame sorption (DAAG) includes columns ct (concentration–time sum), Cultivar (apple cultivar), Dose (injected dose of methyl bromide), and rep (replicate number, within Cultivar and year). Fit a model that allows the slope of the regression of ct on Dose to be different for different cultivars and years, and to vary randomly with replicate. Consider the two models:

Explain (i) the role of each of the terms in these models, and (ii) how the two models differ. Which model seems preferable? Write a brief commentary on the output from the preferred model. [NB: The factor gp, which has a different level for each different combination of Cultivar, year and replicate, associates a different random effect with each such combination.]