On page 15 will be found a group of words ending in _or_, _er_, and
_ar_. These should be taught in groups until they are thoroughly fixed.
Mnemonics may help to establish the correct form. Remind the pupil of
the spelling and pronunciation of _authority_ and he will remember that
_author_ ends in _or_. Likewise _factory_, _inventory_, _oratory_,
_similarity_, etc., help to show him the correct spelling of the shorter
word. Following this drill review the entire page.