Remember that electronegativity measures the type of bond formed. When the electronegativity is above 1.7 it represents an ionic bond when the electronegativity is between 0.4 and 1.7 consists of a polar covalent bond, and when the electronegativity is under by 0.4 the bond is a polar non-covalent, so the answer is A: if the electronegativity difference between two atoms is above 1.7, the bond is ionic.