I got this answer wrong twice

lily88888UID: 2828533

QC investigator: Upon testing samples of products from our supplier that were sent by our field inspectors from various manufactuiring locations, out laboratory discovered that over 20 percent of the samples were defctive. Since our supplier is contractually required to limit the rate of defects among items it manufactures for us to below 5 percent, it has violated its contract with us.

The reasoning in the QC control investigator's argument is flawed in that the argument

B. Presumes, without providing justification, that the field inspectors were just likely to choose a defective item for testing as they were to choose a nondefective item.

D. Overlooks the possibility that the field inspectors tend to choose items for testing that they suspect are defective.

duijinxiaoziUID: 2585955

B的意思是：
选中“ defective” 和 “ 非defective ” 的概率 都是 50%。
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So, laboratory should discovered that 50 percent of the samples were defective.