In Hong Kong the eighth day of the fourth lunar month is a special day, called Bun Festival, many residents and travelers gather at Cheung Chao island to celebrate a unique tradition.
A. which
B. when
C. while
D. as
网友回答
A. which
(答案→)B. when
C. while
D. as
解析：通过分析句子结构，可知这个句子中包含一个定语从句，且关系词在从句中作时间状语，故用关系副词when。