题目选项分析

Although nobody knows when ravens first arrived at the Tower of London, their presence has been all but mandated for approximately 300 years, because a superstition holds that if there are no ravens at the Tower, the entire kingdom will fall.

Although nobody knows when ravens first arrived at the Tower of London, their presence has been all but mandated for approximately 300 years, because a superstition holds that if there are no ravens at the Tower, the entire kingdom will fall.