1. Are there any metro systems?
Or
2. Is there a metro system?
?
Both are possible, depending on how many metro systems you are expecting. (1) would typically be used of a region or country, while (2) would typically be used of a city.
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Both are possible, depending on how many metro systems you are expecting. (1) would typically be used of a region or country, while (2) would typically be used of a city.