Select the most appropriate ANTONYM to replace the highlighted word in the given sentence. "I am astonished to see her mercurial demeanour in making any task a success."

Correct option is D

Explanation of the Correct Answer: · "Mercurial" means unpredictable, changeable, or volatile.
· The antonym should mean steady, unchanging, or constant.
· "Invariable" means unchanging and fixed, making it the best antonym.
Why Are the Other Options Incorrect? · (a) Capricious → Incorrect; it is a synonym, not an antonym.
· (b) Erratic → Incorrect; also means unpredictable, another synonym.
· (c) Fluctuant → Incorrect; means changing frequently, also a synonym.
Thus, the correct answer is (d) Invariable.