The correct answer is: D. no units
Relative permittivity is a dimensionless quantity that is used to compare the permittivity of a material to the permittivity of a vacuum. It is denoted by the Greek letter $\epsilon_r$. The permittivity of a vacuum is a fundamental constant of nature, and it is denoted by the Greek letter $\epsilon_0$. The permittivity of a material is given by the equation:
$$\epsilon = \epsilon_r \epsilon_0$$
Therefore, the relative permittivity is a dimensionless quantity.
Option A is incorrect because the units of farad per meter (F/m) are the units of permittivity.
Option B is incorrect because the units of meter per farad (m/F) are the units of inverse permittivity.
Option C is incorrect because the units of weber per meter (Wb/m) are the units of magnetic flux density.