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In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: A recent experiment held in Japan shows that it is almost impossible for people to walk exactly straight for 60 metres. Tokyo University of Agriculture and Technology found 20 healthy men and asked them to walk as straight as possible to a target 60 metres away at normal speed. Each man had to walk on white paper fixed flat to the floor wearing wet colored socks. The footprints revealed that all walked in a winding rather than a straight line. Researchers found that people readjust the direction of walking every few seconds. The amount of the winding differed from _ to subject. This suggests that none of us can walk in a strictly straight line. We walk in a winding way mainly because of a slight structural or functional imbalance of our limbs . Although we may start walking in a straight line, several steps afterwards we have changed direction. Eyesight helps us to correct the direction of walking and leads us to the target. Your ears also help you walk. After turning around a lot with your eyes closed, you can hardly stand still, let alone walk straight. It's all because your ears help you balance. Inside your inner ear there is a structure which contains liquids. On the sides of the organ are many tiny hair-like structures that move around as the liquid flows. When you spin the liquid inside also spins. The difference is that when you stop, the liquid continues to spin for a while. Dizziness is the result of these nerves in your ear. When you open your eyes, although your eyesight tells you to walk in a straight line, your brain will trust your ears more, thus you walk in a curved line.
Answer: the participants kept readjusting their direction of walking
Output:
The experiment held in Japan proved that _ .