单选题 It can be inferred from the passage that a change in class relationship after the Middle Ages led to greater productivity because______.

A、 freemen had incentives to produce more.
B、 masters had greater incentive to make their workers harder.
C、 slaves never starved, no matter what they produced.
D、 productivity could go in only one direction.

【正确答案】 A

【答案解析】推理判断题。要进行反向推断。在第二段中，作者从理论上解释了社会关系阻碍科学进步的原因。第二段最后一句总结道：特权阶级有时间却没有知识和经验，而劳动阶尽管有知识和经验，却没有incentive。由此可推断出有两个原因造成生产力落后。根据逻辑推理，这种情况的产生，要么是由于特权阶级获取了知识，要么是因为劳动者拥有了动力，所以，选项A是正确答案。