You are given a science question (hard-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.

During an experiment, a class heated a balloon that had an initial circumference of 25 cm. The circumference increased to 27 cm. Which is the best conclusion that can be drawn?
(A) The molecules inside the balloon lost energy to the outside. (B) The molecules inside the balloon gained energy from the heat. (C) The energy of the molecules inside the balloon remained the same. (D) The molecules inside the balloon were escaping outside.
B