Which grammatical error most severely impacts the 'Grammatical Range and Accuracy' score in IELTS Writing and Speaking, beyond simple errors like subject-verb agreement?

✓ Correct Answer: Option D

While all options represent errors, repeatedly using only simple sentences significantly limits the 'Grammatical Range' aspect of the score. To achieve a higher score, candidates must demonstrate the ability to use a variety of complex sentence structures (e.g., compound, complex, conditional sentences) accurately and appropriately. Failing to do so severely restricts the range shown.