Mutant Saccharomyces cerevisiae cells that lack the gene encoding securin can divide more or less normally by mitosis, without significant chromosome segregation defects. Cells harboring a nondegradable version of securin, on the other hand, arrest in metaphase as expected, since they cannot activate separase to enter anaphase. Similarly, cells lacking Cdc20 (an APC/C activator) arrest in metaphase, since they cannot activate APC/C. Finally, cells lacking both securin and Cdc20 arrest in anaphase: they manage to separate sister chromatids, but do not progress much further. These results suggest that in wild-type cells:. A. Degradation of securin is necessary to trigger sister-chromatid separation. B. Degradation of securin is sufficient to trigger sister-chromatid separation. C. Cdc20–APC/C is NOT necessary for sister-chromatid separation. D. Cdc20–APC/C is NOT necessary for later events in anaphase. E. All of the above.