Improve the highlighted part of the sentence. Choose 'No improvement' as an answer if the sentence is grammatically correct.
The effect of the changes was unexpected.

The correct answer is (d) No improvement.
Explanation:
The sentence is already grammatically correct. "The effect" is singular, and "was unexpected" correctly agrees with the singular subject. Therefore, no improvement is needed.
Meanings of all options:
· Has unexpected: Incorrect verb form, should be "has been unexpected."
· Was unexpect: Incorrect form, should be "was unexpected."
· Were unexpected: Incorrect verb form as "effect" is singular, not plural.
· No improvement: The sentence is correct as it stands.