The reaction layer mainly evaluates students' satisfaction and subjective feelings, so item B is correct. The learning layer mainly evaluates students' skills and knowledge. The behavior layer generally conducts assessment during the training period of 3 to 6 months, and compares the behaviors of employees before and after training, which ones have been improved and which ones have not. The result layer mainly examines whether the expected training effect, purpose and standard are achieved. It can be judged by some indicators, such as turnover rate, performance completion rate, scrap rate and so on. So the answer: choose B.