With no explanation, chose the best option from "A", "B", "C" or "D". See also United States v. Morgan, 384 F.3d 1, 6 (1st Cir.2004) (questioning whether plain error was even available, or whether the issue was waived entirely, when a Blakely issue was neither raised below nor initially in this court). Plain error is an extremely deferential standard; errors will be corrected only if “(1) ... an error occurred (2) which was clear or obvious and which not only (3) affected [his] substantial rights, but also (4) seriously impaired the fairness, integrity, or public reputation of judicial proceedings.” Id. (quoting United States v. Duarte, 246 F.3d 56, 60 (1st Cir.2001)). In applying the plain error standard after Blakely, we have held that no plain error occurs where the facts underlying the enhancement _ were undisputed. Savarese, 385 F.3d at 22 (<HOLDING>). We have also noted, and now emphasize, that

A: holding that a defendant who fails to object to an error at a plea colloquy hearing must satisfy the plain error rule
B: holding that a defendant who did not dispute the factual basis underlying the sentence enhancement forecloses a finding of plain error
C: holding that omission was not plain error
D: holding that a sentencing court may warn a defendant of the possibility of a sentence enhancement
B.