Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature and other physical conditions remain unchanged (V = IR). A material or device is said to be "ohmic" if its resistance R is constant and independent of the applied voltage/ current/electric field over a significant range. Statements A, B, and C describe aspects of Ohm's law or materials obeying it. Statement A describes Ohm's law as the proportionality between V and I (though the "always" can be debated depending on interpretation, compared to D it's less definitively wrong). Statements B and C correctly define an ohmic device/material as one whose resistance is independent of the magnitude and direction of the applied potential difference/electric field. Statement D is a universal claim that is false. Many homogeneous materials (e.g., semiconductors, diodes, electrolytes) do not obey Ohm's law. Even ohmic materials like metals can deviate from Ohm's law at very high electric fields or extreme temperatures.