Henry's dog Sparky has been rolling in the mud. Henry must bathe Sparky before the dog gets mud all over the carpet. However, Henry is unable to find the plug for the tub. Sitting on the counter right beside the tub is a fifty-cent piece. In his frustration, Henry fails to see that the coin could be used as an emergency plug for the tub. What happened to Henry? a) He took a heuristic approach. b) He fell prey to the confirmation bias. c) He suffered from mental set. d) He employed representational thought.