Read the following excerpt from a US court opinion:
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file a petition for a writ of habeas corpus in tribal court. Mr. Valenzuela argues that the district court was incorrect. He asserts that he exhausted all tribal court remedies and that “[a]ny further attempts to exhaust tribal remedies would be futile and result in irreparable damage.” Aplt. Br. at 18. First, Mr. Valenzuela argues that he waived his right to appeal in his written plea agreement and therefore had no tribal court remedies to exhaust. We agree with the district court that Mr. Valenzuela’s appeal waiver does not excuse his failure to pursue habeas corpus relief in the tribal court. The appeal waiver did not expressly waive Mr. Valenzuela’s right to collaterally attack his conviction in tribal court. See United States v. Cockerham, 237 F.3d 1179, 1181-83 (10th Cir.2001) . That step was necessary to exhaust Mr.
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What is the most suitable continuation to the opinion? Your options are:
A. holding that under oregon law an agreement must be supported by consideration to be legally enforceable
B. holding appellate waivers are enforceable if invoked by the government
C. holding that waivers of  2255 collateral attack rights must be expressly stated to be enforceable
D. holding federal regulations have the force of law and may create enforceable rights
E. holding that prospective waivers of claims are void as against public policy
Reply with [A, B, C, D, E] only.