Answer:
The thought experiment proposed by Richard Sylvan centers on option d) "The last rider on a trolley heading for a crash."
Explanation: This scenario is known as the "Last Rider" thought experiment, which is a philosophical scenario often used to explore issues related to ethics, moral decision-making, and utilitarianism. It presents a situation where a person is faced with a difficult moral choice, and it prompts discussions about whether the action taken should prioritize minimizing harm, even if that harm is inevitable.