The correct reflexive pronoun for "one" is "oneself", ensuring grammatical correctness.
The correct sentence is:
"One should keep oneself prepared."
Thus, the correct answer is Option A ("One should keep oneself prepared").
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?