Definition: In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.
Input: The Doctor:  I 'm sorry to tell you that Romana can look after herself . We 're Time Lords . Not like those innocents on Atrios , you know . Time Lords , sent by the Guardian to recover the Key to Time .
The Shadow: I know who you are , Doctor , I have always known . I have been waiting for you . I too serve a Guardian , a Guardian equal and opposite in power to the _ one _ you serve . The Black Guardian - he who walks in darkness . And you are in the valley of the Shadow !

Guardian