Final answer:
The best approach to aid participants in solving the "tumor problem" is to provide them with a similar problem they know how to solve and instruct them to use it to find a solution.
Step-by-step explanation:
When participants struggle to solve a problem like the "tumor problem," which option is most likely to help them find a solution? The answer is (d) The experimenter must also present participants with an analogous problem to which they already know the solution and explicitly tell participants to use this analogous problem to help them solve the "tumor problem." By drawing parallels between the known solution of the analogous problem and the current problem, participants can transfer understanding and apply similar problem-solving strategies to reach a solution more effectively.