Which of the Following Best Describes Direct Effect

Which of the following best describes direct effect?

A) It is the making of a decision by general agreement and in the absence of any voiced objection.
B) It is the relinquishment of an obligation owed by another.
C) It is a principle whereby a treaty may be invoked by a private person to challenge the actions of a state that is a party to the treaty.
D) It is a principle that governments must make their rules, regulations, and practices open and accessible to the public and other governments.