Explanation:

 Both (b) & (c). Statement b and c essentially implies the same thing, though they are differently worded. National treatment: Treating foreigners and locals equally – Imported and locally-produced goods should be treated equally — at least after the foreign goods have entered the market. The same should apply to foreign and domestic services, and to foreign and local trademarks, copyrights and patents. National treatment only applies once a product, service or item of intellectual property has entered the market. Therefore, charging customs duty on an import is not a violation of national treatment even if locally-produced products are not charged an equivalent tax. Read more –
https://www.wto.org/english/thewto_e/whatis_e/tif_e/fact2_e.htm