1) Don't take..(my/meine) pen! Take..(your/yeurs)!
2) What was..(your/yeors) mother doing?
3)...farm is as rich as..(our/ours/their/theirs)
4) This offise is..(their/theirs).
5) Those are Victor's books. The books are..(mine/his/hers)

1) Don't take my pen! Take yours!2) What was your mother doing?3) Our farm is as rich as theirs.4) This offise is theirs.5) Those are Victor's books. The books are his.PS правильно пишется yours и mine