Which of the following statements about molecular orbitals are true?

a. A molecular orbital can hold a maximum of two electrons.

b. The number of molecular orbitals formed equals the number of atomic orbitals that are mixed to form the MOs.

c. A bonding molecular orbital will have a lower energy than that of the two atomic orbitals that are mixed to make the MO.

d. Electrons cannot be put in antibonding molecular orbitals.

e. A bonding molecular orbital concentrates electron density in the region between two atoms.