The sentence in which the modifier "far" is used correctly is the following one: Kendra ran farther than Holly. There are a few rules that should be followed when comparing things. For adjectives that are just one syllable you should add -er to the end. As you can see, this is the case with "far" since it is a one-syllable adjective. For two syllable adjectives not ending in -y and for all three-or-more-syllable adjectives, you should use the form more+adjective. Finally, for two-syablle adjectives ending in -y, you should change the -y to -i and add -er to the end.