Silicon, a Semiconductor, Has Four Valence Electrons

Silicon, a semiconductor, has four valence electrons. Titanium, a conductor, also has four valence electrons. Despite both having four electrons, the elements differ in their conductivity because

A) Ti atoms are smaller than Si atoms
B) The band gap energies fall sharply in from the third period to the fourth period on the periodic table
C) Ti has low-lying d orbitals that form a conduction band, Si does not
D) Ti has a larger ionization energy that Si
E) None of the above.