Multiple From Clauses

Use additional from clauses when each element in the source is itself a collection or contains a collection:

IEnumerable<City> cityQuery =
    from country in countries // Here, 'countries' is a collection of 'Country' objects.
    from city in country.Cities // Here, 'Cities' is a collection of 'City' objects.
    where city.Population > 10000
    select city;