Carbon tetrachloride has no net dipole moment because of
A. it's planar structure
B. its regular tetrahedral structure
C. similar sizes of carbon and chlorine atoms
D. similar electron affinities carbon and chlorine:

Hint: If all the dipole moments(bond) are exactly opposite to each other in a molecule or cancel Each Other completely, the net dipole moment of the molecule becomes zero.
 The correct answer is(B).

Complete answer:
In a carbon tetrachloride molecule the geometry of the structure of the molecule is tetrahedral. Chlorine is more electronegative with partial negative charge and carbon carries partial positive charge.
In this regular tetrahedral structure, the bond dipole moment of all the bonds is the same and also all the bonds have a positive vector so they cancel Each Other dipole moment. Hence, the net dipole moment of the molecule is zero or it has no net dipole moment.
Dipole moment of a chemical bond is an entity which is used to measure or calculate the polarity of that Bond within the molecule. Bond dipole moment comes into existence whenever positive and negative charges’ separation occurs in a molecule.
The idea behind the discovery of bond dipole moment is that of an electric dipole moment. Bond dipole moment takes into concern the partial positive and the negative charges.
Diatomic molecules possess only one Bond which can be either single or double, so the net dipole moment of the diatomic molecule is equal to the individual Bond dipole moment.
Polyatomic molecules contain more than one Bond so the net molecular dipole moment of the molecule becomes equal to the sum(vector) of all Bond dipole moments.

Note: The dipole moment of individual bonds of C→Cl in carbon tetrachloride is not zero. Only the net dipole moment of the molecule is zero.