before we move on with the question, we need to check for parallelism.
would have walked and seen have to be parallel.
Have + past participle is the correct form.
1st event- person attacked[ past perfect]
2nd event- clothes torn[past tense]

A. seen a stabbed man crouching on the sofa, whose clothes torn [ you have a past perfect in the sentence. so we need a simple past for a later event.Eliminated!]

B. saw a stabbed man crouching on the sofa, whose clothes were torn [parallelism not maintained. Eliminated!]

C. seen a stabbed man crouching on the sofa, with clothes torn [ you need a past tense and not a preposition. Eliminated!]

D. seen a stabbed man crouching on the sofa, whose clothes were torn [Voila!My answer. Sentence properly maintained.]

E. seen a stabbed man crouching on the sofa, whose clothes have torn[ present perfect is not the required tense. we need past tense. Eliminated!]

Hope this helps!

fibbonnaci wrote:before we move on with the question, we need to check for parallelism.
would have walked and seen have to be parallel.
Have + past participle is the correct form.
1st event- person attacked[ past perfect]
2nd event- clothes torn[past tense]

Nice explanation! Especially liked the above part that you said.