With no explanation, chose the best option from "A", "B", "C" or "D". evidence. Adidas instead argues that this omission is not an automatically reversible error. Similarly, the PTO argues that the Board did not err because it “implicitly found that reducing waste was not a long-felt but unresolved need.” Intervenor Br. 19 (emphasis added). Because long-felt need is indisputably a secondary consideration, see Graham, 383 U.S. at 17-18, 86 S.Ct. 684, our precedent dictates that the Board is bound to fully consider properly presented evidence on the long-felt need for a claimed invention. Recognizing that the Board operates under stringent time con-straintSj we do not hold that it is obliged to explicitly address conclusory and unsupported arguments raised by a litigant. Cf. Fresenius USA Inc. v. Baxter Int’l, Inc., 582. F.3d 1288, 1296 (Fed.Cir.2009) (<HOLDING>). Under the particular circumstances presented

A: holding that a party cannot preserve an argument if it presents only a skeletal or undeveloped argument to the trial court
B: holding that it is the burden of the party who failed to preserve his argument to demonstrate plain error
C: holding that the appellant waived an argument listed only in his summary of the argument
D: holding that a party waives an argument if the party fails to elaborate or provide any citation of authority in support of the argument
A.