Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- 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
 