一级理论和二级理论的区别

As if he knew that Ning Cheng was looking at him, Nian Yan's eyes swept down from the stage and fell on Ning Cheng. He smiled at Ning Cheng, then nodded, and then withdrew his gaze. Ning Cheng also smiled and nodded to Nian Yan. He understood what Nian Yan meant, which was to reassure him....