Please refer to this answer, taken from Crowdflower's FAQ section:
We do our best to ensure that each task has the best possible quality control system in place, but things do slip through the cracks sometimes. If you feel that our system has treated you unfairly, then be sure to contest the question on the feedback page. You may also send us a clear and concise explanation of the problem using the blue "Send Feedback" button at the top right of the interface (next to your accuracy percentage). If we find that you are correct, then we will be sure to forgive you and all other participants that missed the same question. You can contact us at email@example.com.
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