Correct Answer:
B. for
Explanation:
The correct answer is for because the present perfect continuous context requires a preposition that measures a complete duration of time.
- Step 1 (Grammatical Rule): In English grammar, 'for' is paired with a specific numerical duration or block of time (e.g., ten years, three hours), whereas 'since' is reserved for a single starting point in the past.
- Step 2 (Application): Because 'ten years' defines a total accumulated span of elapsed time, 'for' is the only structurally sound choice.
- Incorrect Options:
- since is incorrect because it requires a specific fixed calendar date or point in time (e.g., since 2016).
- from is incorrect because 'from' requires a corresponding 'to' or 'until' to cleanly map out a static time block.
- at is incorrect because 'at' is exclusively used to point out specific clock times or highly localized positions.