The correct answer is D) D and E only. Cargo tanks on barges fitted with goose neck vents and flame screens are limited to carrying grades D and E only, which are the lowest flammability grades of cargo. This is because goose neck vents and flame screens provide a lower level of explosion protection compared to other vent designs, and therefore can only safely handle the least flammable cargo grades. The other answer choices are incorrect because A) and B) would allow for higher flammability grades, which would be unsafe with the limited vent design, while C) would be too broad, as the regulations specifically limit these tanks to D and E grades.