Which reaction below is a physical change?
a. CH4(g) + 2O2(g) → CO2(g) + 2HsO(l)
B.CaO(s) + H2O(l)→ Ca(OH)2(s)
c. H2O (l) → H2O(s)
d. 2HsO (l) → 2H2(g) + O2(l)