Step 1: Understanding customary international law.
Customary international law develops from consistent state practice and the belief that such practice is legally obligatory. This includes both state actions (what states do) and state claims (assertions of rights or duties).
Step 2: Application.
Both state actions and state claims are necessary elements to establish a customary rule.
Step 3: Conclusion.
Hence, the correct answer is (c) both 1 and 2.