He has been absent . . . . . . . . a fortnight.

Answer: Option C

Understanding the Question:
The question asks you to choose the correct preposition to complete the sentence: "He has been absent . . . . . . . . a fortnight." A preposition shows the relationship between a noun or pronoun and other words in a sentence.

Understanding the Options:
* Option A (from): "From" indicates a starting point in time or place.
* Option B (since): "Since" indicates a point in time from which something has continued to the present.
* Option C (for): "For" indicates a duration of time.
* Option D (to): "To" indicates a direction or destination.

Choosing the Correct Preposition:
The sentence talks about how long he has been absent. We need a preposition that shows a duration. "For" is the preposition that shows duration of time. Therefore, "He has been absent for a fortnight" is correct.

Why other options are incorrect:
"From" needs a starting point (e.g., "He has been absent from Monday").
"Since" also needs a specific starting point (e.g., "He has been absent since Monday").
"To" indicates a destination, which doesn't fit the context of absence.