Self-study
All oceangoing ships carry seawater ballast tanks whose weight improves stability. ██ ████████ ███ ██████ ██████ ██████████ █████ ████ ██ ██████ ███ ██ █████ █████ ████ █████ ██ ██████ ███ ████ ████ ████ █████ ██ █████████ ██ █ ███████ ███ █████████ █████ ███ ████ ███ █████ ███ ███ ████ █████████████ █████████ ████ ███ █████████ █████ ████ ███ █████ ██████████ ██████ ███ ██████ ███ ██ ██████████ ████ ███████ █████ ██ ██ █████ ███ ████ ███████████ ██████ ███ █████ ██ █████████ █████ ████████ █████████ ███ ███████ ███ █████████ ███████ ██████ ███████ ██ ███ █████████ █████████
Summary
All oceangoing ships face a problem. To maintain stability, water has to be pumped out of ballast tanks when cargo is loaded/unloaded. But sea creatures that get in the tank during the loading/unloading are deposited later when the cargo is loaded/unloaded and can damage the environment.
The author concludes that one viable way of addressing the problem is to empty and immediately refill the tanks in the midocean.
Why? Because midocean creatures and coastal sea creatures usually can’t survive in one another’s habitats. (The idea is that the coastal creatures would be deposited in the midocean and die; the midocean creatures would be deposited in the coast and die.)
Notable Assumptions
The author assumes that the midocean creatures deposited in the coast would not survive long enough to cause significant damage to the environment.
The author assumes that oceangoing ships are able to empty and then immediately refill the tanks in midocean.
26.
Which one of the following ██ ██ ██████████ ███ ████████ █████████
a
Emptying and refilling ██ ██████████ ██████ ███████ █████ ██ ████████ █████ ██████ ██ █████ ████ ██ ███ █████████ ███████ ██ ██████████ ███ ███████ ██ █ ███ ███████ ███ ██████ ████ ███ ██████
Not necessary. The author’s theory allows for creatures that could cause environmental damage to get into the tanks. But the author believes that when those creatures are deposited in a different environment, they’d die before actually causing significant environmental damage.
b
An oceangoing ship's ███████ █████ █████ ██ ███████ ███ ████████ ██ ████████ ████ ██ ██████████ ██ ████ ███ ███ ████ █████
Not necessary, because the author doesn’t suggest anything about the specific conditions under which tanks could be emptied and refilled in midocean. If this could occur under conditions other than calm air and flat seas, that doesn’t undermine the author’s reasoning.
c
Sea creatures have ███████ ██ █████ ███████ ██████████ █████ ██ █ ███ ████████ ██████ ████ ████ ████ ████ ██ ███████ ██ ████ ███████ █████ ██████ ████ █████████ █████ ██ ██████████ ██████
Not necessary, because the author’s argument isn’t based on what has actually happened in the past. The author is theorizing about a potential solution based on where midocean creatures and coastal creatures can survive. This doesn’t require any assumption about what has rarely occurred or commonly occurred in the past.
d
Currently, seawater is ██████ ████ ██ ███ ██ ███ ███████ █████ ██ ██████████ █████ ██ ████████ ██████ █████████ ████ ████ █████████ ██ ███████ ██████
Not necessary, because even if there are other times when the tanks are emptied and refilled, that doesn’t undermine the author’s reasoning. The author happens to be talking about a problem resulting from emptying/refilling the tanks when unloading/loading cargo, but if emptying/refilling occurs at other times, the author’s solution could still address any problems resulting from sea creatures getting into the tank during those other emptying/refilling occurrences.
e
There are at █████ ████ ██████████ █████ █████ █████████ █████ ██ ██████████ ██████████ █████ ████████ ███ █████████ █████ ███████ █████ ██ █████████
Necessary, because if it weren’t true — if there are NO oceangoing ships whose stability could be adequately maintained while emptying/refilling in midocean — then the author’s solution is not a “viable” way of addressing the problem. If oceangoing ships could not maintain adequate stability by using the author’s proposed solution, then it’s not a realistic option.