With no explanation, chose the best option from "A", "B", "C" or "D". We already have concluded that the instructional error, combined with the prosecutor’s improper closing argument, affected Vega’s substantial rights. See supra Part 111(A)(1). It would have been possible for the government to argue that these errors tainted the verdict against Vega only on count 5, not on count 4, but the government essays no such argument. It does not contend that the errors, in combination, were harmless as to either count. Under the circumstances of this case, we choose not to do the government’s homework. See United States v. Rodríguez-Marrero, 390 F.3d 1, 18 (1st Cir.2004) (noting that the court of appeals may deem any harmless error argument waived if not briefed by the government); see also United States v. Rodríguez-Cortes, 949 F.2d 532, 542-43 (1st Cir.1991) (<HOLDING>). At any rate, the evidence against Vega was

A: holding that the failure to identify or argue an issue in an opening brief constitutes waiver of that argument on appeal
B: holding that failure to develop a legal argument supporting a claim results in waiver of the claim
C: holding that failure to brief an argument constitutes waiver
D: holding that the governments failure to argue harmless error results in a waiver of the argument
D.