The correct answer is D.
The sentence “They have spotted me in the crowd” is in the simple past tense. This means that the action of spotting happened at a specific point in the past. The other options are all in the future tense, which means that the action of spotting has not yet happened.
Option A, “I am spotted by them in the crowd,” is in the present passive voice. This means that the focus of the sentence is on the person being spotted, not on the person doing the spotting. The sentence could be rewritten as “They spot me in the crowd.”
Option B, “I will have been spotted by them in the crowd,” is in the future perfect passive voice. This means that the action of spotting will have happened by a specific point in the future. The sentence could be rewritten as “They will have spotted me in the crowd by the time you get there.”
Option C, “I would have been spotted by them in the crowd,” is in the past perfect passive voice. This means that the action of spotting would have happened by a specific point in the past, but it did not happen. The sentence could be rewritten as “If I had been there, they would have spotted me.”