Most major air pollutants cannot be seen, although large amounts of them, concentrated in cities, are visible as smog. (Option E).
Sentence correction or sentence improvement is a type of grammatical practice where a sentence is given with a word or a phrase that requires grammatical changes or improvement.
Now,
Hence, Option E is the most appropriate, i.e., Most major air pollutants cannot be seen, although large amounts of them, concentrated in cities, are visible as smog. (Option E).
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