单选题 After making observations for a week in the plant, the industrial engineer made a number of very constructive suggestions in an oral report to the manager.
A. careful B. cautious
C. deserved D. helpful

【正确答案】 D
【答案解析】constructive意为“建设性的、有助益的”。四个选项的含义分别是：“认真的”、“小心谨慎的”、“当之无愧的”、“有帮助的”，故D为正确答案。