With respect to graphite and diamond, which of the statement(s)...

(a) Diamond is harder than graphite. (b) Graphite is good conductor of electricity as each carbon is attached to three C-atoms leaving one valency free, which is responsible for electrical conduction, while in diamond, all the four valencies of carbon are satisfied, hence insulator. (c) Diamond is better thermal conductor than graphite. Whereas electrical conduction is due to availability of free electrons; thermal conduction is due to transfer of thermal vibrations from atom to atom. A compact and precisely aligned crystal like diamond thus facilitates fast movement of heat. (d) In graphite, $\mathrm{C}-\mathrm{C}$ bond acquires double bond character, hence higher bond order than in diamond.