The correct answer is: A. Even after worked in the office
The sentence should be: Even after working in the office for as many as fifteen years, he still does not understand the basic objectives of the work.
The verb “work” is conjugated correctly in the past participle form (“worked”) because it is being used as an adjective to modify the noun “office.” However, the preposition “in” is incorrect because it is used to indicate a location, not a period of time. The correct preposition to use in this case is “for.”
The sentence is also missing a comma after the phrase “for as many as fifteen years.” This comma is necessary to separate the independent clause (“he still does not understand”) from the prepositional phrase (“for
as many as fifteen years”).Finally, the sentence is missing a period at the end. This is necessary to indicate that the sentence is complete.