From the given sentence, form a feminine noun from the masculine noun given:
The author was on the verge of a new idea.
The answer to the given sentence is Option D, Authoress.
As per the question, the sentence would have the male gender noun to be replaced by the feminine noun, without dropping the vowel, and then adding the syllable ‘-ess’. The male gender noun, ‘Author’ is used for a person who has written a book (writer), of which the feminine counterpart is ‘authoress’, that is option D, which follows the rule of the question and means the same as well. While Option B, Writeress, is a word which does not exist, Option A, Writer is a common gender noun. Option C, Poetess, is actually the female gender noun of which the male counterpart will be ‘poet’.
Thus, Option D, Authoress, is the correct answer.