You did not give the choices but I can teach you the concept behind this problem. Polarity is brought about by the imbalance of charges. It is manifested by the large difference between the electronegativities of the elements involved. The more electronegative element would be assigned with the partial negative (δ-) sign, while the less electronegative element would be the partial positive sign (δ+). The larger the difference of the electronegativities, the more polar the bond is.