Why I Flunked English

We’ll begin with a box, and the plural is boxes;
But the plural of ox became oxen not oxes.
One fowl is a goose, but two are called geese,
yet the plural of moose should never be meese.
You may find a lone mouse or a nest full of mice;
yet the plural of house is houses, not hice.
If the plural of man is always called men,
why shouldn’t the plural of pan be called pen?