![](https://cos-cdn.shuashuati.com/pipixue-wap/2020-1230-1107-53/ti_inject-812ce.png)
Why does the article refer to polychlorinated biphenyls?
A.
to give an example of a product thought to be harmless that was later found to be toxic
B.
to give an example of a product that has many uses
C.
to explain another new technology
D.
to give an example of a product created with nanomaterials