The correct answer is mysteries.
A. minor aspects
B. shady retreat
The correct answer is (D) Mysteries; secrets; information known only to those involved, particularly involving alchemical research. Also, a secret and powerful remedy, or a great secret of nature, which alchemists attempted to discover.
Arcana, the plural form of Arcanum, comes from Latin arcere (to shut in).
Examples of use:
- Arcana that captivated alchemists included the change of metal to gold.
- Finding an elixir of life was among the arcana that preoccupied alchemists.