Answer the questions based on the following passage: To study chromatid adhesion, Paliulis mastered the high art of manipulating two infinitesimal glass needles to impale each of two sister chromatids in cultured grasshopper cells at the appropriate time in cell division. Then, she would ever-so-gently apply force to pull them apart. Upon release, if they remained apart it revealed they were separated; but if they snapped back together the researchers would know the chromatids were still attached. Paliulis was a Duke graduate student when she performed the experiments, but is now a postdoctoral fellow at the University of North Carolina at Chapel Hill The experiments revealed that the chromatids are attached to one another, but that they initially separate at their centers, zipping apart until they are entirely separate. Then, they can be drawn to the opposite poles of the dividing cell. The experiments also revealed that it is the erosion of linkages between the chromatids, and not any tension exerted by the spindle, that causes the chromatids to separate. Also intriguing, found the researchers, was that the chromatids mysteriously remained stuck to one another at a time when biochemical analysis could not detect any cohesin proteins in the cell. Nicklas believes that the twin chromatids may still have some entanglements between the corresponding DNA strands on each chromatid. DNA, which makes up genes in the cell, replicates itself as a central process in chromosome duplication. "So, we're left with the mystery of what molecules hold the chromatids together at this point in cell division," Nicklas said. "But that's the usual outcome of work in my laboratory and a sign that we're doing good science since we raise new questions. We lay the mechanistic groundwork for the molecular explanations that have to be made. So, our colleagues who do molecular work are both provoked and challenged by us," he said. Source: http://www.sciencedaily.com/releases/2005/01/050111180610.htm a) Describe how these scientists believe the sister chromatids are separated. during mitosis. b) Explain why these scientists think that they are doing "good science".