As one of its main pillars, countries that live under a democratic system are free to elect their political leaders through the act of vote, usually in a secret, free and peaceful process. While voting is conceived as a civil duty, it is not an obligation, and members of the population can decide to exercise their right to abstain as a way to express their political will.
Therefore, the answer is: A. In some countries, citizens have the right to vote but choose not to.