To capricious means to be unpredictable or prone to frequent changes.
Option A is correct as the word "fickle", too, means to be prone to frequent changes. It is another word for "capricious.
Option B is incorrect as the word is completely unrelated to the given word. To be calm is to without nervousness, anger or other such strong emotions. It has nothing to do with the given word.
Option C is incorrect for the same reason as B. To be careful means to be cautious or to avoid danger or harm. It has nothing to do with being capricious.
Option D is incorrect as the word is completely unrelated to the given word. Forgetful is the habit of not remembering things.