abstract opening sentences from a single issue of Nature Subject

• Mechanisms facilitating A are incompletely understood.
• The characteristics of B are not fully defined.
• The molecular basis of C remains vague.
• The mechanisms responsible for D remain enigmatic.
• The influence of E1 on E2 remains uncertain.

Someone should create an opening-sentence-o-matic poker machine. I would include "elucidated" as one of the final word options.