The most polar bond would have the highest difference in electronegativity values between the two atoms. Since fluorine has the highest value of electronegativity (3.98), the least electronegative atom would make the most polar bond with it. Chlorine is very electronegative so we can eliminate that one. Between carbon and silicon, silicon has the lower number (1.9 versus 2.2), so the correct answer would be B.
To find the element with the highest electronegativity, always remember that electronegativity increases across a period and decreases down a group. This means the the most electronegative elements are in the upper right hand corner of the periodic table and the least electronegative elements are in the lower left hand corner. Since sulfur is the furthest to the right and furthest up on the periodic table of the four choices, the correct answer is A.