Choose the correct word(s) for the blank in this sentence: Nikola Tesla ____ for Thomas Edison for a short time in the 1880s, but the two men disagreed on which type of electricity was better and safer.

The only verb tense that is grammatically correct in this sentence is the past tense worked. The clues in the sentence would are the other past tense verb, disagreed, and the date of the 1880s, which has long since passed.