(D) The two words here have a time relationship: a harbinger comes before an event and helps to foretell or predict it (crocuses are harbingers of spring), while the aftermath is what follows an event and bears its traces. In the same way, a forebear is an ancestor, one who comes before a certain person or time; a descendant follows or comes after.
HARBINGER: a person or thing that comes before to
announce or give an indication of what
follows; herald
AFTERMATH: a result or consequence, esp. an
unpleasant one
Precursor: a substance that precedes and is the
source of another substance
Ancestor: any person from whom one is descended,
esp. one earlier in a family line than a
grandparent; forefather; forebear
Omen: a thing or happening supposed to foretell
a future event, either good or evil;
augury
Genesis: the way in which something comes to b;
beginning; origin [G3] the first book of the
Bible, giving an account of the Creation:
abbrev
Descendant: a person who is an offspring, however
remote, of a certain ancestor, family,
group, etc.
Prediction: the thing predicted or foretold