Natural disturbances, including hurricanes and earthquakes, have affected coral reefs for millions of years. They are typically acute but have short-lived (19) ----. Reef areas (20) ---- human influences often recover within a few years 21) ---- water and substratum quality remain high. Indeed, acute natural disturbances can actually help (22) ---- iversity on coral reefs by knocking back dominant species and allowing (23) ---- competitive species to re-establish themselves.
19.
A) products
B) conditions
C) concerns
D) effects
E) explanations
20.
A) down to
B) up to
C) up against
D) out of
E) away from
21.
A) so that
B) unless
C) though
D) if
E) whether
22.
A) to have maintained
B) maintaining
C) having maintained
D) to be maintained
E) to maintain
23.
A) much
B) little
C) as
D) less
E) least
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