We know that the electron clouds of two atoms overlapping is a bond, because that signifies that the electrons are being shared in a bond.
So, I'm going to go through some definitions of these different types of bonds, because they have very specific circumstances.
A hydrogen bond is a bond between an electronegative atom and a hydrogen molecule (which is not what this question says, this isn't stated anywhere).
A dipole is a difference in electron density on two different atoms (so this isn't even close to what the question is stating, a dipole is not even a bond)
An ionic bond is an unequal sharing of electrons between two atoms (because the question doesn't state this specific fact, then it can't be this option).
By process of elimination, we know the answer is covalent bond, but just in case, we can also look at the definition of a covalent bond: a bond that involves the sharing of electrons between atoms.
That is exactly what the question is asking for! Therefore, your answer is d. covalent bond
