The Configuration of All the Naturally Occurring -Amino Acids $- \mathrm { CH } _ { 2 } \mathrm { SH }$

Multiple Choice

The configuration of all the naturally occurring -amino acids is as follows:
All but one of the naturally occurring -amino acids have the S configuration at the asymmetric carbon. In the one amino acid that has the R configuration, the "R" group is
(a)
$- \mathrm { CH } _ { 2 } \mathrm { SH }$
(b)
$- \mathrm { CH } _ { 2 } \mathrm { OH }$
(c)

(d)
$- \mathrm { CH } _ { 2 } \mathrm { CH } _ { 2 } \mathrm { SCH } _ { 3 }$

A) group (a) .
B) group (b) .
C) group (c) .
D) group (d) .
E) None of these has the R configuration.