1．Ancient China was a place ________ states were often at war with each other.
答案：where
2．October 1,1949 was the day ________ the People's Republic of China was founded.
答案：when
3．I don't know the reason ________ she looks unhappy today.
答案：why
4．The man ________ is shaking hands with my father is a policeman.
答案：who
5．This is the scientist ________ name is known all over the country.
答案：whose
6．Guilin is a city ________ has a history of 2 000 years.
答案：which/that
