Final answer:
The correct possessive form for the phrase B) 'the skins of the potatoes' is the potatoes' skins.
Step-by-step explanation:
The correct possessive form for the phrase 'the skins of the potatoes' is option B: the potatoes' skins. When a noun is plural and ends in -s, the apostrophe is placed after the final -s.
In this case, 'potatoes' is the plural form of potato, so we add the apostrophe after 'potatoes'. This indicates that the skins belong to the potatoes.