If An airline is "countable", this means that there MUST be a flight attendant present on the plane, whose sole job is to count: In case of IEnumerable, only lines up to the element of interest will be read from the file. In case of ToList call over the enumerable, https://c-object-kullan-m08528.blogofoto.com/59218127/c-ienumerable-nasıl-kullanılır-ile-ilgili-detaylı-notlar