The correct answer is A) A tank of pyridine may be used to separate a tank of carbon disulfide from a tank of diisopropylamine. This is correct because carbon disulfide and diisopropylamine are incompatible cargoes that require separation by an intermediate tank or void space. Using a tank of pyridine as an intermediate barrier between the two incompatible cargoes is an acceptable way to meet the separation requirements. The other options are incorrect because B) does not correctly identify the tank arrangements, C) requires two barriers instead of just one intermediate tank, and D) allows the incompatible cargoes to be carried in tanks with a common header vent, which is not permitted.