The correct answer is D) branch lines. The main underdeck pipeline on a tankship is connected to individual tanks by branch lines. These branch lines allow the cargo to be transferred from the main pipeline to the individual cargo tanks. This is in accordance with standard tankship design and operation regulations. The other answer choices are incorrect because: A) Tank drops are not the connections between the main pipeline and individual tanks. B) Line drops are also not the correct term for these connections. C) Crossovers typically refer to connections between parallel pipelines, not from the main pipeline to individual tanks.