PrepTest 137

Incorrect. While compost that is 80% organic material isn't the best compost, that doesn't guarantee that it smells of ammonia or that it hasn't decomposed sufficiently. Only an ammonia smell is established as being sufficient to conclude that the compost hasn't sufficiently decomposed, but there's nothing suggesting we can make that determination here.

Incorrect. Compost with these two features won't be the best compost, but it could still be good compost and thus appropriate for drainage and fertility.

Incorrect. There's no statement that establishes anything as sufficient for compost to be good compost, so this answer isn't supported by the stimulus.

Incorrect. The stimulus only discusses sufficient decomposition, not complete decomposition, so this answer is out of scope.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Good garden compost → Used for soil drainage and fertility
Best garden compost → 40-60% organic AND Dark brown
Compost with strong ammonia smell → not Used for soil drainage and fertility

Answer Anticipation:
First, note that we didn't include the last clause in our Summary. The rest of the statements are all conditional statements (they present connections that are certain), and that one isn't, so it's unlikely to factor into the correct answer.

Since we have several conditional statements, the correct answer is likely to combine them in some way to form an inference. Looking at the statements we have, there are only two that have a shared term—the first and last both talk about using compost for soil drainage and fertility. They're on the same side of the conditional arrow, but they're negated, so we should take the contrapositive of one (doesn't matter which), chain them together, and then take the contrapositive of that:
Ammonia-smelling → not Used for drainage/fertility → not Good compost
Good compost → Used for drainage/fertility → not Ammonia-smelling

We can try to make that second conditional work with the others, but there's no real shared term, so let's see if what we have gets us the right answer.

Answer Explanation:
Regardless of the color, the conditional chain we built states that compost smelling of ammonia isn't good compost, so this answer is correct. Compost that smells of ammonia shouldn't be used for drainage/fertility, whereas all good compost can be, supporting this conclusion.

Key Takeaway:
Whenever a stimulus talks with certainty and brings up the same or similar terms, you can use conditional notation to approach it. When you have several conditional statements in a Must Be True question, any statement that isn't conditional (and isn't meant to "trigger" a conditional rule) is unlikely to factor into the correct answer.