Consider the following statements about lipids and identify the correct ones.
I. Fatty acids are simple lipids with a carboxyl group attached to an R group, which can vary in length from 1 to 19 carbons.
II. Saturated fatty acids contain one or more C=C double bonds, while unsaturated fatty acids do not have any double bonds.
III. Glycerol, a trihydroxy propane, can combine with fatty acids to form monoglycerides, diglycerides, and triglycerides.
IV. Fats and oils are distinguished by their melting points, with oils having a higher melting point and remaining solid in winter.
V. Phospholipids, like lecithin found in cell membranes, contain phosphorus and a phosphorylated organic compound.