a controlled single-variable laboratory test support through evidence from numerous observations proposal of alternative explanations with predictive value a full-scale replication of each event in the proper sequence
I gave my students this multiple choice question: The hypothesis of an expanding universe required which type of validation before being accepted as a significant part of scientific theory?

Only one answer is correct among these 4 choices:
- a controlled single-variable laboratory test
- support through evidence from numerous observations
- proposal of alternative explanations with predictive value
- a full-scale replication of each event in the proper sequence

Could you tell me which one is correct?

support through evidence from numerous observations