Can you identify the grammatically incorrect sentence from each set?

Option 3 is the grammatically incorrect sentence. Let's see why.

When we use demanding words like "demand," "insist," or "suggest," the verb that follows must be in its base form (called the subjunctive mood) — no -s, -ed, or -ing.

So "leaves" should be "leave."

✅ "He demanded that she leave immediately."

Just like: "I suggest that he study harder" (not "studies").

Now let's quickly confirm the other options are correct:

Option 1 → Uses the past unreal conditional (third conditional) correctly. "Had asked" and "would have helped" pair up perfectly to talk about something that didn't happen in the past. ✅

Option 2 → After "as if," we use "were" (not "was") for unreal or imaginary situations. Since she isn't actually royalty, "were" is the right choice. ✅

Option 4 → Correctly uses the past perfect tense ("had gone") to show that one past event (their leaving) happened before another past event (our arriving). ✅