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       Mixing main idea with details: Questions asking the main idea or primary purpose of the passage have answer choices that are true but aren’t the main idea. These are trap answers. For example, a passage may describe light pollution from cars or streetlights that obscures stars at night. The main idea isn’t the car headlights or streetlights: It’s the overall effect on nighttime visibility. Double-check the first and last sentences. Is the author asking for increased funding or a course of action? Is the passage challenging a common notion? If you know why the author is writing this, you’ll know the primary purpose of the passage and not be distracted by detail answers.One strategy is to work main idea or primary purpose questions last, especially with a long Reading Comprehension passage. Because you can go back and forth through the questions, you can work them in any order. As you answer the detail questions, you learn more about the main idea; then you can go back and answer that main idea question. Just don’t forget it and move forward, leaving that question unanswered.

       Mixing cause-and-effect relationships: Answer choices typically mix up the cause-and-effect relationships of details in the passage. If the tide comes in because of the moon, for example, and this causes all the ships to rise, the question will check your understanding of what caused what to happen. Skim the passage for key words relating to the cause-and-effect described in the question. From the preceding example, look for the words moon, tide, and ships. Find the discussion of these events, and make sure the answer choice reflects the events discussed in the passage.

       Mixing in your own knowledge: You may know something about the topic at hand. If you’re like most people, you add detail based on your own knowledge and expertise from other things that you’ve read. Sometimes, these details tempt you to choose an answer that’s true by your understanding but wrong per the passage. Be careful not to mix your own knowledge with what’s in the passage. I had a student who was a chemistry major work on a Reading Comp passage on chemistry, and she vehemently disagreed with what was in the passage. She was probably right — but she got all the questions wrong, based on what she thought it should be instead of what the passage said.

       Microbiological activity clearly affects the mechanical strength of leaves. Although it cannot be denied that with most species the loss of mechanical strength is the result of both invertebrate feeding and microbiological breakdown, the example of Fagus sylvatica illustrates loss without any sign of invertebrate attack being evident. Fagus shows little sign of invertebrate attack even after being exposed for eight months in either a lake or stream environment, but results of the rolling fragmentation experiment show that loss of mechanical strength, even in this apparently resistant species, is considerable.

       Most species appear to exhibit a higher rate of degradation in the stream environment than in the lake. This is perhaps most clearly shown in the case of Alnus. Examination of the type of destruction suggests that the cause for the greater loss of material in the stream-processed leaves is a combination of both biological and mechanical degradation. The leaves exhibit an angular fragmentation, which is characteristic of mechanical damage, rather than the rounded holes typical of the attack by large particle feeders or the skeletal vein pattern produced by microbial degradation and small particle feeders. As the leaves become less strong, the fluid forces acting on the stream nylon cages cause successively greater fragmentation.

       Mechanical fragmentation, like biological breakdown, is to some extent influenced by leaf structure and form. In some leaves with a strong midrib, the lamina breaks up, but the pieces remain attached by means of the midrib. One type of leaf may break cleanly, whereas another tears off and is easily destroyed after the tissues are weakened by microbial attack.

       In most species, the mechanical breakdown will take the form of gradual attrition at the margins. If the energy of the environment is sufficiently high, brittle species may be broken across the midrib, something that rarely happens with more pliable leaves. The result of attrition is that where the areas of the whole leaves follow a normal distribution, a bimodal distribution is produced, one peak composed mainly of the fragmented pieces, the other of the larger remains.

       To test the theory that a thin leaf has only half the chance of a thick one for entering the fossil record, all other things being equal, Ferguson (1971) cut discs of fresh leaves from 11 species of leaves, each with a different thickness, and rotated them with sand and water in a revolving drum. Each run lasted 100 hours and was repeated three times, but even after this treatment, all species showed little sign of wear. It therefore seems unlikely that leaf thickness alone, without substantial microbial preconditioning, contributes much to the probability that a leaf will enter a depositional environment

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