Rank the following compounds in terms of their retention times on a Carbowax GC column (a polar one):

a. propionic acid (b.p. = 141 0C);
b. isopentyl alcohol (isoamyl alcohol) (b.p. = 113 0C);
c. isopentyl acetate (isoamyl acetate) (b.p. = 142 0C);
d. 3,4-dimethylheptane (b.p. = 140 0C).