quenya_grammar1-3  Exercise 3: "Every plural ends in -r"
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Correction: there are two general plural endings, -i and -r (lassë -> lassi;
alda -> aldar), a partitive plural -li (lasseli, aldali), and a dual ending
-t (lasset). The formal register adds -í and -lí.

Left unexplained by the sources (any two):
  - which noun types take -i and which take -r (the page says "the type of
    the noun" without a full rule)
  - exactly when the partitive -li is required
  - the rules for the long -í of the formal register (unpublished)
  - missing forms in some paradigms (nér, cas)