Which of the following shows a pronoun and antecedent agreement?

a. "friendship with oneself is all important because without it, you cannot be friends with anyone else in the world."
b. "friendship with yourself is all important because without it, one cannot be friends with anyone else in the world."
c. "everyone thinks of changing the world, but no one thinks of changing themselves."
d. "everyone thinks of changing the world, but no one thinks of changing himself."