Concept:When a sentence uses the indefinite pronoun "one" as its subject, the possessive form that agrees with it is "one's".
Explanation:In formal English, "one" is singular and refers to people in general.
Therefore, any possessive linked to "one" must also be "one's".
For example: "One should always do one's best."
Option A, "his", refers specifically to a male person.
Option B, "their", is plural and does not agree with the singular "one".
Option C, "your", directly addresses the reader, which changes the subject.
Only Option D, "one's", keeps the pronoun agreement correct and matches the formal tone of the sentence.
Thus, the sentence is best completed by "one's".
Answer:D. one's