1.45     explain how the uses of diamond and graphite depend on their structures, limited to graphite as a lubricant and diamond in cutting.

Although there are covalent bonds joining the carbon atoms in each layer, the layers of atoms in graphite are only weakly attracted together (dotted lines in the above diagram) and can easily slide over one another. This sliding means graphite can behave as a lubricant.

Diamond is strong because it has a giant covalent structure consisting of carbon atoms linked by very strong covalent bonds only.  This makes it hard, so good for cutting hard substances.