21. It is very difficult to prove today that a painting done two or three hundred years ago, especially one without a signature or with a questionably authentic signature, is indubitably the work of this or that particular artist. This fact gives the traditional attribution of a disputed painting special weight, since that attribution carries the presumption of historical continuity. Consequently, an art historian arguing for a deattribution will generally convince other art historians only if he or she can persuasively argue for a specific reattribution.

Which one of the following, if true, most strongly supports the position that the traditional attribution of a disputed painting should not have special weight？

（A） Art dealers have always been led by economic self-interest to attribute any unsigned paintings of merit to recognized masters rather than to obscure artists.

（B） When a painting is originally created, there are invariably at least some eyewitnesses who see the artist ac work, and thus questions of correct attribution cannot arise at that time.

（C） There are not always clearly discernible differences between the occasional interior work produced by a master and the very best work produced by a lesser talent.

（D） Attribution can shape perception inasmuch as certain features that would count as marks of greatness in a master's work would be counted as signs or inferior artistry if a work were attributed to a minor artist.

（E） Even though some masters had specialists assist them with certain detail work, such as depicting lace, the resulting works are properly attributed to the masters alone.

22. Much of the best scientific research of today shows that many of the results of earlier scientific work that was retarded in its time as good are in fact mistaken. Yet despite the fact that scientists are above all concerned to discover the truth, it is valuable for today's scientists to study firsthand accounts of earlier scientific work.

Which one of the following, if true, would best reconcile the two statements above？

（A） Many firsthand accounts of earlier, flawed scientific work are not generally known to be mistaken.

（B） Lessons in scientific methodology can be learned by seeing how earlier scientific work was carried out, sometimes especially when we results of that work are known to be incorrect.

（C） Scientists can make valuable contributions to the scientific work of their time even if the results of their work will later be shown to be mistaken.

（D） There are many scientists today who are not thoroughly familiar with earlier scientific research.

（E） Some of the better scientific research of today does not directly address earlier scientific work.

23. Teachers are effective only when they help their students become independent learners. Yet not until teachers have the power to make decisions in their own classrooms can they enable their students to make their own decisions. Students' capability to make their own decisions is essential to their becoming independent learners. Therefore, if teachers are to be effective, they must have the power to make decisions in their own classrooms.

According to the argument, each of the following could be true of teachers who have enabled their students to make their own decisions EXCEPT：

（A） Their students have not become independent learners.

（B） They are not effective teachers.

（C） They are effective teachers.

（D） They have the power to make decisions in their own classrooms.

（E） They do not have the power to make decisions

24. Dr. Ruiz： Dr. Smith has expressed outspoken antismoking views in public. Even though Dr. Smith is otherwise qualified, clearly she cannot be included on a panel that examines the danger of secondhand cigarette smoke. As an organizer of the panel, I want to ensure that the panel examines the issue in an unbiased manner before coming to any conclusion.

Which one of the following, if true, provides the strongest basis for countering Dr. Ruiz' argument that Dr. Smith should not be included on the panel？

（A） A panel composed of qualified people with strong but conflicting views on a particular topic is more likely to reach an unbiased conclusion than a panel composed of people who have kept their views, if any, private.

（B） People who hold strong views on a particular topic tend to accept new evidence on that topic only if it supports their views.

（C） A panel that includes one qualified person with publicly known strong views on a particular topic is more likely to have lively discussions than a panel that includes only people with no well-defined views on that topic.

（D） People who have expressed strong views in public on a particular topic are better at raising funds to support their case than are people who have never expressed strong views in public.

（E） People who have well-defined strong views on a particular topic prior to joining a panel are often able to impose their views on panel members who are not committed at the outset to any conclusion