These are all semi-regular nouns. They're not completely irregular (i.e., child, man, woman, ox, etc.), but they don't form plurals by simply adding -s.
Think of each noun, regular or irregular, as having four forms:
desk (s), desk's (s. poss.)
desks (pl), desks' (pl. poss.)
So ... I'll do the first one for you:
Now ... how will you write the other three forms of the other two? If you're not sure, be sure to use a dictionary to find the plural -- http://www.dictionary.com
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