No improvement to this sentence is necessary. It makes perfect sense on its own and sounds right. "Either" always takes an "or" else the word wouldn't make sense, as it's meant to contrast binary options.
eg.
I'm either going to eat food or drink water.
The correct answer is B. I took the test and D was wrong
The answer is: [D]: "will have" .
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"On Friday Vanessa <u> will have </u> been travelling for a month."
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The correct answer is 3) The narrator has been insulted many times and vows revenge against Fortunato.
At one point in time when he felt that he had been insulted, the narrator decided that enough was enough and that he would have his revenge.