Here's a problem to solve: A group of Canada geese left a Florida lake in the spring. The geese arrived at a Maine lake 2,000 km away in 40 days. If the geese traveled at a constant rate, how far did the geese travel on the first day?

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

- A: 5 km
 
- B: 20 km
 
- C: 40 km
 
- D: 50 km
 