The word "incomplete" starts with the vowel sound "in."
The general rule for articles:
Since "incomplete" begins with the vowel sound "in," the correct article is "an."
The correct sentence is:
"It is an incomplete answer."
Thus, the correct answer is (B) "an".
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?