Question: After observing several dogs running, students ask the following question: Do dogs with long hair run faster than dogs with short hair? How can the students best answer their question?

  Options: 
 A. record the weights and heights of many dogs
 B. measure the speeds and hair lengths of many dogs
 C. research to find the type of dog with the longest hair
 D. race one long-haired dog against one short-haired dog 
Answer: B