I cannot understand where the apostrophe goes when using the possessive.
Is it grass's or grasses'? Is it human's or humans'?
Thanks in advance,
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How many grasses are there?
If you're looking at your lawn you might say "The grass's color is not good." But in another context you might say (admittedly a poor example) "The implication of grasses' oxygen production on the earth's atmosphere is significant."
How many humans?
"That human's intelligence is incredibly low." "The impact of humans' presence on the earth's climate is significant."
Singular nouns, uncountable nouns, proper nouns, even if they end in s, even if the s is silent - add 's.
grass -> grass's
DeJarlais -> DeJarlais's
Plural nouns - add single apostrophe at the end. Same for the rare case of proper plural nouns. The pronunciation doesn't change. If that would create clarity issues you can say belonging to the grasses or by the grasses instead.
grasses -> grasses'
Joneses -> Joneses'
There are a few irregular plurals in English that don't end in s. Those take a 's.
children -> children's
geese -> geese's
A few more exceptions are described here for classical names.