Read the following excerpt from a US court opinion:
```
Johnston argues, as he did in the postconviction court, that he is exempt from execution under the Eighth Amendment to the United States Constitution because his severe mental illness places him in the same category as those whose executions are barred because they were under the age of eighteen at the time of the murder or are mentally retarded. The court below denied relief, finding Johnston’s claim was procedurally barred for not having been raised on direct appeal or in prior posteonviction proceedings and because, under this Court’s precedents, mental illness is not a per se bar to execution. We agree with both these conclusions. Relying on the reasoning behind the United States Supreme Court’s rulings in Roper v. Simmons, 543 U.S. 551, 125 S.Ct. 1183, 161 L.Ed.2d 1 (2005)  and Atkins v. Virginia, 536 U.S. 304, 122
```
What is the most suitable continuation to the opinion? Your options are:
A. holding the death penalty unconstitutional for defendants under age eighteen at the time of the crime
B. holding the death penalty unconstitutional for mentally retarded defendants
C. holding that mandatory life imprisonment without parole for those under the age of eighteen at the time of their crimes violates eighth amendment
D. holding the eighth and fourteenth amendments forbid imposition of the death penalty on offenders who were under the age of eighteen when their crimes were committed
E. holding that the death penalty is unconstitutional as applied to juvenile defendants
Reply with [A, B, C, D, E] only.