This paper explores whether the open-end questions, which are constructed to develop critical thinking (CT) in China's English textbook, are effective. All the 405 questions are examined and categorized into non-CT group and CT group, which includes lower-stage CT and higher-stage CT. Findings reveal that most of them fall into non-CT group, therefore ineffective to enhance CT. Some of them are non-text based. Others are unjustifiable. Still others are not hierarchically distributed. Corresponding modifications are then suggested for the improvement of ineffective questions. It enlightens later researchers with the conclusion that effective questions should be text-based, text-justified, integrated with a reader's own judgment and hierarchically distributed.