Given the task definition and input, reply with output. This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: In contrast to the Fed, the ECB normally does not buy bonds outright. The normal procedure used by the ECB for manipulating the money supply has been via the so-called refinancing facilities. In these facilities, bonds are not purchased but used in reverse transactions: repurchase agreements, or collateralised loans. These two transactions are similar, i.e. bonds are used as collaterals for loans, the difference being of legal nature. In the repos the ownership of the collateral changes to the ECB until the loan is repaid.
Who loses ownership of the collateral until the debt is paid?