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：考查从句连接词。选A的话，是it was...that强调句型，去掉it was和that之后，April 29, 和Prince William and Kate Middleton walked into the palace hall of the wedding ceremony无法连接起来，时间前面缺少介词on，排除A；since常构成it has/had been+一段时间 since+含有过去时的句子，这里的April 29, 是时间点，排除C；before常构成it is/was/will be+一段时间before+句子，April 29, 是时间点，排除D。选B的话，是由when引导的定语从句，主句是It was April 29, 。故选B。
