Explanation:

- Original Sentence: "They greet me cheerfully every morning."

- Active Voice: The subject (They) is performing the action (greet).

- Option 1: "Every morning I was greeted cheerfully."

- Past Tense Passive: This suggests it happened in the past, which changes the original meaning.

- Option 2: "I am greeted cheerfully by them every morning."

- Present Tense Passive: This maintains the original meaning but in passive voice.

- Correct Transformation: The action is performed on the subject (I).

- Option 3: "I am being greeted cheerfully by them every morning."

- Present Continuous Passive: Implies a continuous action, which alters the original aspect slightly.

- Option 4: "Cheerful greeting is done by them every morning to me."

- Awkward Construction: Slightly unnatural phrasing in English.