a)  Incorrect.  CCl₄ is a tetrahedral molecule.  Each of the bonds is polarized toward the chlorine atom.  Adding together any two bond dipoles
            gives a subtotal sum halfway between them directed away from the central carbon atom.  Adding together the other two bond dipoles gives a
            second subtotal sum halfway between them directed away from the central carbon atom.  These two subtotal sums are exactly opposite each
            other (tail-to-tail) and will therefore cancel each other out making the molecule nonpolar.  CHCl₃ is also a tetrahedral molecule.  Each of the
            three C-Cl bonds is polarized toward the chlorine atom while the C-H bond is polarized toward the carbon atom.  Adding together two C-Cl
            bond dipoles gives a subtotal sum halfway between them directed away from the central carbon atom.  Adding together the third C-Cl bond
            and the C-H bond dipoles gives a subtotal sum which won't cancel out the other subtotal sum (since the combination is different) thus the
            molecule is polar.