Answer:
c. Electrons are shared, but they aren't shared evenly
Step-by-step explanation:
Pure (non polar) bonds have a low electronegativity difference of 0.0 - 0.4 which allows electrons to be shared.
Polar bonds have a high electronegativity difference of 2.0 4.0 so rather than sharing the electrons, the electrons will be transferred to one atom only and will stay there.
Covalent bonds have a electronegativity difference between these two types of bonds (0.4 - 2.0) so electrons are shared but not equally, meaning they are shared between the two atoms but stay at one atom for a longer period of time than the other.