"what makes a bond polar"?
a. one atom attracts shared electrons more strongly than the other atom
b. one atom has transferred its electrons completely to another atom
c. a sea of electrons has been created between the elements
d. two atoms are sharing electrons with equal attraction

The answer to your question is: letter A.

Explanation:

A Covalent bond polar is between 2 non metals where one atom is bigger than the other one so the distribution of charges creates this polarity.

A. One atom attracts shared electrons more strongly than the other atom  This is the correct definition of bond polar, one element is bigger and stronger than the other element.

B. One atom has transferred its electrons completely to another atom  This definition is incorrect, it is the definition of ionic bonding.

C. A sea of electrons has been created between the elements  This definition is incorrect for the polar bond, it describes a metallic bonding.

D. Two atoms are sharing electrons with equal attraction This definition is incorrect for a polar bond, but is the correct definition for nonpolar bonding.