Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

The tranches in a collateralized mortgage obligation (CMO) that are most likely to provide protection for investors against both extension and contraction risk are:
Option A:planned amortization class (PAC) tranches.
Option B:support tranches.
Option C:sequential-pay tranches.

Answer: A