With no explanation, chose the best option from "A", "B", "C" or "D". 556 U.S. 396, 406, 129 S.Ct. 1696, 173 L.Ed.2d 532 (2009). Based on the particular facts of this case, we cannot hold that the error was harmless because the Board has not yet adjudicated Mrs. Reliford’s accrued benefits claim against the proper factual background. See Gambill v. Shinseki, 576 F.3d 1307, 1311 (Fed.Cir.2009) (per curiam) (“Harmless error is fully applicable to veterans’ claims cases, subject to the same principles that apply generally to harmless error analysis in other civil and administrative cases.”) (citing Sanders, 556 U.S. at 406, 129 S.Ct. 1696); Wagner v. United States, 365 F.3d 1358, 1365 (Fed.Cir.2004) (“Where the effect of an error on the outcome of a proceeding is unquantifiable, however, we will not speculate as to what the outcome might have (1993) (<HOLDING>); cf. Beverly v. Nicholson, 19 Vet.App. 394,

A: holding that this court must remand to the bia to allow it to address in the first instance an issue that it has not yet considered
B: holding that the boards finding that a matter was not before it because a substantive appeal had not been filed was error and determining that because a timely nod had been submitted and the ro never responded by issuing an soc as required by law and regulation the proper remedy was to vacate the board decision as to the matter and remand to the board for appropriate procedural compliance specifically the issuance of an soc
C: holding the board must either obtain a waiver or determine whether a claimant will be prejudiced by the boards adjudication of a question or issue in an appeal not otherwise decided by the ro otherwise it must remand for the ro to decide the question in the first instance
D: holding that this court has discretion to either address or remand arguments presented to it in the first instance provided it otherwise has jurisdiction over the claim
C.