Final answer:
Phalloidin binds specifically to actin filaments, so when attached to a fluorescent dye and added to cell cultures, fluorescence would be observed in the actin filaments.
Step-by-step explanation:
When phalloidin is covalently attached to a fluorescent molecule and added to dividing, ciliated cells in culture, the fluorescence should be localized in the actin filaments of the cells when observed using fluorescence microscopy. Phalloidin is a toxin that binds specifically to actin filaments, which are part of the cytoskeleton of eukaryotic cells. Therefore, the correct answer to where the fluorescence would be localized after using phalloidin linked to a fluorescent dye is (c) Actin filaments.