Step 1: Understanding Fartlek training.
Fartlek training is a method of training that combines continuous running with intermittent bursts of speed. The training method was developed by Gösta Holmér, a Swedish coach, in the 1930s. The term "Fartlek" means "speed play" in Swedish.
Step 2: Conclusion.
The correct answer is (A) Sweden, as the Fartlek training method was developed in Sweden.
Final Answer: Sweden.