Convert singular to plural
Mathematica, 9 bytes
Pluralize

Yes, there is a built-in for this!
Sample output
Pluralize[&quot;car&quot;]


cars

Pluralize /@ {&quot;bus&quot;, &quot;potato&quot;, &quot;knife&quot;, &quot;penny&quot;, &quot;exception&quot;, &quot;wolf&quot;, &quot;eye&quot;}


{&quot;buses&quot;, &quot;potatoes&quot;, &quot;knives&quot;, &quot;pennies&quot;, &quot;exceptions&quot;, &quot;wolves&quot;, &quot;eyes&quot;}