PrepTest 154

Incorrect. This has two issues: it's too strong, and it's speculative. Speculation about the future is always suspicious in Must Be True answer choices, because it's very tough to prove that a statement about something that hasn't happened yet is true. In this case, it's impossible, since the stimulus tells us no lichens can excrete, so there's no way this could be a proven, Must Be True answer.

Incorrect. Also too strong. It says "indicates," as in, always. Not true according to the premises; some factor other than air quality might be responsible for the return of lichens to an area. This might be okay if it said "in some cases, the return of lichens may indicate . . . " but as-is, it's out.

Incorrect. Again, too strong. The absence of lichens could conceivably indicate another problem. Nothing about the stimulus suggests they are ONLY ever harmed by bad air.

Incorrect. This could be true, or it could be false. None of the premises even touch on this, so, while it's an interesting thing to maybe Google later, it isn't a must be true answer.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Ooh, interesting, though sad for the lichen: every lichen is composed of two symbiotic partners, a photosynthetic organism and a fungus. Lichens absorb minerals from air, rainwater, and their growing surfaces, but they have no ability to excrete what they've absorbed. Some of them are susceptible to absorb toxins, for instance in polluted air. These toxins can damage both the fungus and the photosynthetic organism.

Answer Anticipation:
Even though we do have a couple of strong statements, the portion where pollution comes in is weak. "Some" are susceptible and toxic compounds "can' damage the symbiotic partners. So we're either looking for something strong that simply rephrases one of the strong premises, e.g., "No lichen is composed solely of a single organism," or something weak that relates to how pollution can affect certain lichens. As with many "most strongly supported" Must Be True questions, they're probably going to try to tempt us with trap answer choices that are too strong for the premises given.

Answer Explanation:
Nice weak logical force with "can cause problems," not specifying how likely or how severe these problems would be. This is supported by the stimulus, which indicates that the toxins absorbed from polluted air can damage the lichens. Exactly what we wanted.

Key Takeaway:
Don't let the presence of one or two strong statements in a MBT:MSS stimulus throw you off. It's still easier to prove a weak conclusion than a strong one, so check the weaker conclusions against the premises first. You can probably eliminate at least 2-3 answer choices on every MSS question just by looking for those that are too strong.