Which of the following substances undergoes a phase change from solid to liquid by breaking strong covalent bonds?
Buckminsterfullerene (C60C_{60}C60)
Potassium fluoride (KFKFKF)
Silicon dioxide (SiO2SiO_2SiO2)
Tetraphosphorus decoxide (P4O10P_4O_{10}P4O10)