The correct answer is C) Each of the cargoes must be segregated from the other by at least two barriers. This is correct because the International Maritime Dangerous Goods (IMDG) Code requires multiple-product tankships carrying incompatible cargoes, such as crotonaldehyde, phosphoric acid, and morpholine, to have at least two barriers of segregation between the different cargo tanks. This is to prevent the accidental mixing of these hazardous materials, which could lead to dangerous chemical reactions. The other answer choices are incorrect. A) is incorrect because the minimum protective clothing for phosphoric acid may require more than just goggles or a face shield. B) is incorrect because the compatibility of valve materials depends on the specific cargo and its properties. D) is incorrect because the "cancer hazard" warning is not a standard requirement for these cargoes.