Which of the following statements about secondary succession is true? a.
Secondary succession occurs in ecosystems that have no vegetation.
b.
Secondary succession affects ecosystems that are already established.
c.
Ecosystems require pioneer species to undergo secondary succession.
d.
Secondary succession can occur in areas without soil.

Answerjoe ran 130 yards;

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The first immigrants to settle in what is now the united states were the ancient ancestors of modern native americans. the precise routes of those first north american immigrants are disputed, but there is no uncertainty about the fact that every human being on the continent is either a recent immigrant or a descendant of earlier immigrants. since the first immigrants came here from asia more than thirteen thousand years ago, there have been four large and easily recognizable modern waves of immigrants into the united states.