Answer: Option D
Solution:
In the sentence "You have finished...last," the correct preposition to use is at
.
So, the complete sentence is: "You have finished at
last."
The preposition "at" is used to specify a particular point in time or a specific moment when something happened or was completed. In this sentence, "at last" means that you completed something after a period of time or effort, emphasizing the sense of relief or accomplishment.
Therefore, the correct answer is Option D: at
.