..., whose ball I found. (Clearly, there is a mistake at the beginning of the sentence but the context helps to identify the correct relative pronoun.)
His last book, which I didn't read, was very successful.
I don't know which way to go.
Which of the Beatle's album is your favourite?
<u>Who, which and whose are relative pronouns. </u>
Who only refers to people. It is used in 2 because it refers to <em>"The guy"</em>
Whose refers to people or things. It is used in 1 because it refers to <em>"the man"</em>. The <em>"house"</em> belongs to <em>"the man"</em>. In sentence 4, <em>"whose" </em>indicates that the <em>"ball"</em> belongs to somebody.
Which refers to objects and animals. It refers to the "pen" in sentence 3, to <em>"his last book"</em> in sentence 5 and to <em>"the Beatle's album"</em> in 7.