Answer:
The correct answer is suffix IBLE.
Step-by-step explanation:
Suffixes "able" and "ible" are added to a word as part of a morphological process to change their meaning and category.
In the case of "able", its root is always a full word as in the adjective "enjoyable" which root is the verb "enjoy".
Instead, the suffix "ible" is added to roots which are not a full word as in the adjective "incredible".