which statements about the negotiation for making treaties are correct?

A、 Negotiations between representatives of the parties are to be carried out before the conclusion of the treaty.
B、 Representatives should be fully accredited and given sufficient authority to conduct negotiations, and conclude and sign the treaty.
C、 The authority accorded to the representatives is contained in a formal document known as ·full powers）.
D、 1n practice, a committee is always set up to investigate the validity of the accreditation of all delegates who participated in the negotiations for creating anInternational convention.