As securitization deal contains three tranches as shown below. The spread above Libor indicates the initial yield offered on each tranche:

Tranche X

Libor +2,000 bp

Tranche Y

Libor +60 bp

Tranche Z

Libor +250 bp

The mezzanine tranche is mostly likely

1. Tranche X
2. Tranche Y
3. Tranche Z
4. None of the above since the mezzanine tranche typically does not offer any yield