Concept:The underlined word is "gradual", which means slow and taking place by degrees.
We need the word that is most nearly opposite in meaning and fits the gap correctly.
Explanation:"Gradual" describes an action or change that happens slowly, step by step over time.
Thus, the opposite should describe something that happens suddenly and without warning.
"Abrupt" means sudden and unexpected, making it the best opposite of "gradual".
The other options are not suitable because "anticipated" means expected, while "unhappy" and "unpleasant" describe feelings or qualities rather than manner of occurrence.
Therefore, the correct word to fill the gap is "abrupt".
Answer:A. abrupt