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.

Which of the following type of debt obligation most likely protects bondholders when the assets serving as collateral are non-performing?
Option A:Covered bonds
Option B:Collateral trust bonds
Option C:Mortgage-backed securities

Answer: A