【正文】
when B. while C. if . since ( )4. — Do you know ______ before? — In the People’s Hospital. A. where is Tingting’s father working B. where did Tingting’s father work C. where Tingting’s father is working D. where Tingting’s father worked ( )5. She is among those Americans who interested in Chinese history. A. is B. are C. was D. were Key: Unit 3 Ⅰ . 1. express 2.