Question ID:PT89 S3 Q20 Passage:This passage was adapted from an article published in 2000.Competition to make computer chips smaller and, consequently, faster and more efficient has driven a technological revolution, fueled economic growth, and rapidly made successive generations of computers obsolete. Yet at the current rate of progress this march toward miniaturization will hit a wall by about 2010‚ for many, an unthinkable prospect. The laws of physics dictate that, with current methods, properly functioning transistors‚ the electronic devices that make up computer chips‚ cannot be made smaller than 25 nanometers (billionths of a meter). In living cells, however, natural chemical processes efficiently and precisely produce extremely complex structures below this size limit, so there may be hope of using some such processes to yield tiny molecules that can either function like transistors or be induced to combine with other materials in carefully controlled ways to construct whole nanocircuits. Much current research is aimed at harnessing DNA to this end, but materials chemist Angela Belcher and physicist Evelyn Hu are investigating a different molecular pattern maker: peptides, amino acid chains that are shorter than proteins.The project grew out of Belcher's doctoral research on abalone. Her research group discovered in the mid-1990s that a specific peptide causes calcium carbonate to crystallize into the structure found only in the tough abalone shell. From that discovery, Belcher and Hu, Belcher's postdoctoral adviser at the time, realized that if they found peptides able to direct the crystal growth of the semiconductor materials that form transistors, they might have a tool for building nanoscale electronics. However, no known peptide was able to bind to semiconductor materials to cause the development of particular crystalline structures as some peptides did with calcium carbonate. So Belcher, Hu, and their colleagues grew a random assortment of one billion different peptides and tested whether any of them bound to silicon, gallium arsenide, or indium phosphide crystals‚ three widely used semiconductor materials. They found a few peptides that not only bound exclusively to one of the crystals in the experiment but also latched onto a particular face of the crystal. Through a process resembling accelerated evolution, they developed additional related peptides from those that had the initially promising characteristics.Hu says that in order to use such a method to assemble a set of circuit-building tools it would be necessary to identify many additional organic compounds that bind to circuit-component materials. The group is making progress on that quest. As they have expanded their targets to 20 more semiconductor materials, their cache of crystal-manipulating peptides has ballooned into the hundreds. They are also designing new peptides that bind to two different crystals at once, acting as a daub of glue. It will take that kind of finesse at the nanoscale to produce self-assembling circuits. Stem:The primary role of the first two sentences of the passage is to help the reader understand Correct Answer Choice:BChoice A:why research of the sort done by Belcher and Hu was not previously undertaken by other researchers Choice B:the purpose and importance of the research that Belcher and Hu have undertaken Choice C:the skepticism with which some members of the scientific community have greeted Belcher and Hu's research Choice D:a commonly held viewpoint against which Belcher and Hu's research is directed Choice E:a hypothesis that Belcher and Hu's research is designed to test