In this task you need to give reasons to justify the pronoun coreference relations. Each of the provided inputs contains a sentence with a target pronoun and a question about how to justify the coreference between a noun phrase and the target pronoun. Good practices involve the discussion about how the descriptions attached to the targeted pronoun relate to the noun phrase candidate in the question. The reasoning could come from one or multiple following knowledge types about commonsense: First: 'Property', the knowledge about property of objects (e.g., ice is cold). Second: 'Object', the knowledge about objects (e.g., cats have ears). Third: 'Eventuality', the knowledge about eventuality (e.g., 'wake up' happens before 'open eyes'). Forth: 'Spatial', the knowledge about spatial position (e.g., object at the back can be blocked). Fifth: 'Quantity', the knowledge about numbers (e.g., 2 is smaller than 10). Sixth: all other knowledge if above ones are not suitable. Write the sentence in natural language.

[Q]: Sentence: Sam pulled up a chair to the piano, but it was broken, so he had to stand instead.
 Question: Why does the 'it' refer to the chair?
[A]: Because He wanted to sit in the chair. If he had to stand, the chair had to be broken.


[Q]: Sentence: Adam can't leave work here until Bob arrives to replace him. If Bob had  left home for work on time, he would be here by this time.
 Question: Why does the 'he' refer to bob?
[A]: Because Adam was already at work, and Bob was the one that needed to arrive.


[Q]: Sentence: The drain is clogged with hair. It has to be removed.
 Question: Why does the 'It' refer to the hair?
[A]:
Because You can more easily remove hair from a drain than the drain itself.