The correct option is A CH3F
The carbon-halogen bonds (apart from the carbon-iodine bond) are polar, because the electron pair is pulled closer to the halogen atom than the carbon. This is because (apart from iodine) the halogens are more electronegative than carbon. Shorter the bond length, stronger the bond. Hence C-F bond is the strongest among the four. Hence, the Carbon-Fluorine bond is strongest.