Which factor causes vegetation belts to form according to altitude on mountains?

Correct answer: Climate change with altitude

Direct answer: Option A, climate change with altitude. As altitude increases on a mountain, air temperature generally decreases, and moisture, pressure and exposure can also change. These changes create different environmental belts at different heights. Plants suited to warm lower slopes may be replaced by temperate forests, grasslands or sparse alpine vegetation higher up, depending on the mountain and region. The reasoning is: altitude rises; temperature and related moisture conditions change; plant requirements differ; vegetation forms zones. Option A is correct. Option B is wrong because equal market distance is a human-economic condition and does not create natural altitude belts. Option C is wrong because language has no direct role in plant adaptation to height. Option D is wrong because road width does not determine mountain climate or vegetation. The precise sequence varies with latitude, slope and rainfall, so do not memorise one universal list for every mountain. Memory cue: climb upward, climate changes, vegetation changes.