You will be given a definition of a task first, then some input of the task.
You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

The hypothesis of an expanding universe required which type of validation before being accepted as a significant part of scientific theory?
(A) a controlled single-variable laboratory test (B) support through evidence from numerous observations (C) proposal of alternative explanations with predictive value (D) a full-scale replication of each event in the proper sequence
Output:
B