听一段材料，回答下面几个小题。
For what reason did so many people gather on the Golden Gate Bridge?
A.They wanted to use the opening of the bridge.
B.They wanted to walk across the bridge.
C.They wanted to get involved in celebrating the 50th birthday of the bridge.
When did the bridge walk begin?
A.It began at the time when the sun was rising.
B.It began at the time when the sun was setting.
C.It began at the time when the moon was rising.
How long did the party last?
A.It lasted four hours.
B.It lasted the whole day.
C.It lasted half a day.