Self-study
A mass of "black water" containing noxious organic material swept through Laurel Bay last year. ████ ██████████ ███████ ████ ████ █████ ███ █ █████████ █████████ ███ ██████████ ███████████ ███ █████ █████ ██████████ █████ ███ ████ ███████ ██ █████ ██ ███ ████ █████████ ██████ ██ █████ ████ ████ ████ ████ ███ █████████ ████ ██████████ ████ ██ ████ █████ █████ ██████████ ███ ██████ ███ ███ ███████ ██ ███ ███ █████ ████ ██████ █████████ ██ ███ ████ ██ ███ ████ ███ ██████████
Summary
The author concludes that the black water did not reach last year’s intensity any time in the past 200 years.
What makes the author think this?
Because the black water completely wiped out mounds of coral that were more than two centuries old.
Notable Assumptions
The author assumes that if the black water had reached last year’s intensity some time in the last 200 years, then the coral mounds that were destroyed last year would have been destroyed earlier. (This overlooks the possibility that the coral mounds might have been able to survive even if they had been hit by black water of last year’s intensity in the past.)
11.
Which one of the following ██ ██ ██████████ ████████ ██ ███ █████████
a
Masses of black █████ ████ ██ ████ ████████ ████ ██████ ████ ████ ███ ███ ████ ██████████ ████ ████ ████ █████ ███ ██████████
Not necessary, because the author is not committed to the view that the black water has ever hit the bay before. The conclusion is that EVEN IF it has hit the bay before, it wasn’t of last year’s intensity in the last 200 years. That conclusion does not assert that the black water has hit the bay before.
b
Every species of █████ ██ ███ ███ ███ █████████ ██████ ██ ███ ████ ██ █████ █████ ████ █████ ██ ████ █████
Not necessary, because the reasoning is based on the effects of black water on five species of coral. We don’t know that these constitute “every species” of coral in the bay, nor does any part of the argument rest on the idea that those are all the species.
c
The mass of █████ █████ ████ █████ ███████ ███ ███ ████ ████ ███ ███ ████████ ███ █████ ██ ██████ ███████ ████ █████ ███ ██ ██████
Not necessary, because whether other plants/animals have been hurt is irrelevant. The argument is based on what occurred to five species of coral in the bay and what we can infer based on the damage to those species.
d
The mounds of █████████████ █████ ████ ████ █████████ ████ ███ ██ ██████████ ███████ █████████ ████ ██████ ███ █████ █████ █████ ██ ████ █████
Necessary, because if it were not true — if the mounds of centuries-old coral that were destroyed WERE in especially fragile condition just before the black water hit the bay last year — then that fragile condition could explain how the black water might have hit the bay with the same intensity in the past 200 years but still not have destroyed the coral mounds. In other words, the negation of (D) would show that the fact the coral mounds had been around over 200 years does not show that the black water has never hit at last year’s intensity in those 200 years. In previous years, the coral mounds might have been sturdier, allowing it to withstand destruction from previous black water phenomena.
e
Older specimens of █████ ██ ███ ███ ████ ████ ██████████ ██ ██████ ████ ███ ██████ ██ █████ █████ ████ ████ █████ ██████████
Not necessary, even if older specimens were NOT more vulnerable than young specimens, we already know the black water wiped out five species of coral and destroys coral mounds, and the author can still draw reasonable inferences from the fact the coral mounds were over 200 years old. What age category of coral was more or less vulnerable doesn’t undermine the argument.