The correct answer is: D. They will have been felicitated by now.
The sentence “By now the winners will have been felicitated” is in the future perfect passive voice. This means that the action of felicitating (congratulating) the winners will have been completed by a specific time in the future. The time in the future is indicated by the phrase “by now.”
The other options are incorrect because they are not in the future perfect passive voice. Option A, “They will have felicitated the winners by now,” is in the future perfect active voice. This means that the action of felicitating the winners will be completed by a specific time in the future, but the focus is on the person or people who will do the felicitating. Option B, “They will felicitate the winners now,” is in the simple present tense. This means that the action of felicitating the winners is happening now. Option C, “The have felicitated the winners by now,” is in the present perfect tense. This means that the action of felicitating the winners has been completed at some point in the past and the result of the action is still true in the present.
In conclusion, the correct answer is: D. They will have been felicitated by now.