He was seenplayed the piano by me yesterday .这个需要强调 by me,因为不能确定是谁看到.He was seen playing the piano when I came in .这个不需要强调 by me,因为是我进来时看到的,所以不用太烦琐的强调.
答案:He was seen played the piano by me yesterday He was seen playing the piano when I came in不一定啊He was seen play the piano yesterdayHe was seen playing the piano when I came in不要用by me 了不需要强调被“我 ”看见 了
