Explanation:

- The original sentence, "Ritu goes to Singapore for her holidays last December," is grammatically incorrect because "goes" is present tense, conflicting with "last December," which indicates past action.

- Option 1: "was going to Singapore"

- This suggests a continuous action in the past but doesn’t fit with a completed action like "last December."

- Option 2: "went to Singapore"

- Corrects the tense to simple past, aligning with "last December," indicating the action was completed then.

- Option 3: "has gone to Singapore"

- This is present perfect, suggesting the action has relevance to the present, which doesn't align with "last December."

- Option 4: "had gone to Singapore"

- Past perfect implies there is another past action, which isn't present in the sentence.

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