问题补充：
It was April 29, Prince William and Kate Middleton walked into the palace hall of the wedding ceremony.
A. that
B. when
C. since
D. before
答案：
A. that
(答案→)B. when
C. since
D. before
解析：句意：四月29日，威廉王子和凯特米德尔顿步入了皇宫大厅举行了结婚仪式。由备选答案可以判断出本题考察从句。又由于空前为四月29日名词，且这个名词在后面的从句中时间状语，把先行词April29,带入定语从句中：Prince William and Kate Middleton walked into the Palace hall of the wedding ceremony on April 29,,因此可以判断出先行词在从句中作时间状语，所以这是个定语从句，故选B。A.that在定语从句中要作主语或宾语，而C项和D项是引导时间状语从句的，所以答案要选B。
