of which,in which,at which點用?

the first word (of, in, at) is related to the phrasal verb in the sentence

e.g. The book in which politicians unfolded their stories was a bestseller.
this means, politicians unfolded their stories in the book. the book was a bestseller.
"in which" means "in (the noun before it)"

e.g. This is the corner at which the body is found.
this means, the body is found at this corner.

2011-10-23 15:33:05 補充：
no not phrasal verb, but the verb + preposition