The monoterpenoid "rose oxide" (systematic name: tetrahydro-4-methyl-2-(2-methylpropenyl)-2H-pyran or IUPAC name: 4-methyl-2-(2-methylprop-1-en-1-yl)oxane) consists of a set of four stereoisomers. Each stereoisomer has its own fragrance, and, perhaps surprisingly, humans have developed a different sensitivity ("odor threshold") for each of them.
stereoisomer fragrance odor threshold

(2R,4R)-(-)-rose oxide floral, green, herbal, minty, fruity 160 ppb
(2S,4S)-(+)-rose oxide floral, green, herbal, fruity, rose, citrus 80 ppb
(2R,4S)-(+)-rose oxide floral, green, herbal, hay, earthy, heavy, sweet 50 ppb
(2S,4R)-(-)-rose oxide floral, green, clean, sharp, light, rose, sweet 0.5 ppb

(a) Draw the skeletal structure of (2R,4R)-(-)-rose oxide.

(b) Draw the skeletal structure of the enantiomer(s) of (2R,4R)-(-)-rose oxide.

(c) Draw the skeletal structure of the diastereomer(s) of (2R,4R)-(-)-rose oxide.