James wants to know which brand of shoe will help him run faster. He thinks the more expensive shoe should be the one that helps him run faster. He tries three different types of running shoes. He runs one lap on the track with pair of shoes ( shoe A) and times how long it takes. He rests for 15 minutes. Then, he tries on another of shoes (shoe B) and runs a lap around the track, while timing how long it takes. He rests for 15 minutes before repeating the lap with the last brand of shoes (shoe C). Which type of investigation did he plete ?