The correct answer is "Group II. When the root is a full word except for a final e, the forms usually are spelled with -able"
Explanation:
The passage presented in the question explains the basic rules for adding the suffix "-able" to a root word or basic unit that forms words, for doing this, there are eight different rules that define the correct way to add this suffix mainly based on the features of a word. In the case of the word "desire" this word is a root by itself which means it cannot be reduced to smaller particles and this word ends in "-e", also the correct form of adding the suffix "-able" is in the form "desirable" which means the final "e-" is omitted and the suffix is added. Therefore, this word belongs to the rule "Group II", because as desire words of this group are full words excerpt by the "-e" that need to be omitted to add the prefix.
