Which of the following best describes downstream on demand label distribution?

An LSR answers requests for label mappings immediately, without waiting for a label mapping from the next-hop.

An LSR advertises label mappings to all peers for which it might be a next-hop for a given FEC.

An LSR distributes a label mapping for a FEC when it has been requested to do so.

An LSR propagates a label mapping downstream for a FEC. only if it has a label mapping for the FEC's next-hop.