He recalls that 12 years ago when he returned to Taiwan and delivered a lecture on the latest developments in astronomy in English, the students in the audience could all understand. But last semester when he lectured at Tsing Hua, he could tell by the looks on their faces that many students didn't understand what he was saying. In his next lecture he had no choice but to switch to Chinese.
他記得，十二年前回國時曾以英文演講天文學的最新發展，台下學生大都能聽得懂，但上學期他在清大演講，看看學生的表情他就知道很多人聽不懂，第二次演講不得不改用中文。