He went to Beijing at the end of September, ________ there was a grand celebration for new China's 60^th birthday on National Day．

1. A.
   when
2. B.
   which
3. C.
   where
4. D.
   that

 He went to Beijing at the end of September, _________ there was a grand celebration for new China’s 60^th birthday on National Day.

A. when                        B. which                      C. where                      D. that