Article 26 VCLT codifies the maxim:

Question

Accepted Answer

D. PACTA SUNT SERVANDA — every treaty in force is binding upon the parties and must be performed by them in GOOD FAITH

1. Article 26 VCLT: 'Every treaty in force is binding upon the parties to it and must be performed by them in good faith.'
2. The Latin maxim PACTA SUNT SERVANDA ('agreements must be kept') is the foundational principle of treaty law.
3. Article 27 VCLT adds that a party may not invoke the provisions of its internal law as justification for its failure to perform a treaty.
4. This rule is itself a rule of customary international law applicable even to non-VCLT parties.
5. Hence option B is correct.
_Source: UN Charter 1945 / Vienna Convention on Law of Treaties 1969 / ICJ Statute / ARSIWA 2001 — Vienna Convention on the Law of Treaties 1969, Article 26_

Answer

audi alteram partem — the right to be heard before any treaty obligation arises (cf. Vienna Convention on the Law of Treaties 1969, Article 26)

Answer

lex specialis derogat generali — special law derogates from general law (cf. Vienna Convention on the Law of Treaties 1969, Article 26)

Answer

actio personalis moritur cum persona — personal actions die with the person (cf. Vienna Convention on the Law of Treaties 1969, Article 26)