LSAT 92 - Section 1 - Question 06

This is a Must Be True, Except question.

Four answers must be true on the basis of the information in the stimulus. The correct answer could be false.

The stimulus tells us that wildlife experts are adding lime to water to counteract the harmful effects of acid rain. How exactly does lime help? First, it neutralizes acid and thus prevents some damage. Second, it also helps to restore the health of some lakes where life has already been damaged by acid. Note the causal language, not that this affects the correct answer.

Next, specific details about this treatment. If a lake is treated with lime, this treatment must be periodic. That’s a conditional claim. Why? Because water in the lake is constantly being replaced and that has the effect of carrying away whatever lime we put in there. That’s a causal claim. How periodically? That we don't know. But we are told that if a lake's water is replaced more than once every six months, then we're not going to use lime because it's too expensive. That's another conditional claim followed with a causal explanation. This makes sense because the more frequently water in the lake is replaced, the more frequently we have to add lime to it. The lakes where the water is being replaced more than once every six months are apparently too expensive.

Answer Choice (A) says if the lake is a candidate for liming, its water is replaced every six months or less often. This must be true. This is simply the contrapositive of the last statement in the stimulus. Note that negation of “more often than once every six months” is “once every six months or less frequently.”

Answer Choice (B) says in some lakes, if liming is to be successful over the long term in counteracting the harmful effects of acid rain, liming must be repeated at intervals. This also must be true for it is simply a restatement of a conditional from the stimulus. The stimulus states lakes in which lime is used must be treated “periodically,” which just means “repeated at intervals.”

Correct Answer Choice (C) states unlimed lakes in which the water is replaced frequently are less likely to be harmed by acid rain than those lakes in which water is replaced infrequently. This is simply an appeal to our common sense. It is entirely unsupported by the information in the stimulus and therefore could be false. We know from the stimulus that acid rain damages lakes. We also know that adding lime helps to protect and restore those lakes. (C), however, talks about unlimed lakes. It tries to compare two different kinds of unlimed lakes, one where the water is replaced frequently versus the other where the water is replaced infrequently. (C) says the former is less likely to be harmed by acid rain. Again, no information above supports this statement. But our common sense wants to say this is true because we think that if water gets replaced, it should carry the acid away as well, which should be better for the health of the lake. That sounds reasonable and it may in fact be true in the world. But that is irrelevant. The question stem asked for valid support from the statements in the stimulus.

Answer Choice (D) says liming can be effective even if it is used after some life in a lake has been killed by acid rain. This must be true. It is simply what it means to “restore the health of some lakes where life has already been harmed by acidification.”

Answer Choice (E) says if a lake's water is replaced frequently, it may not be economical to attack the effects of acid rain there by liming. This also must be true. Depending on how frequently, it may in fact not be economical. And we know exactly how frequently because the stimulus tells us: more than once every six months.