Complex sentence: The best-known of Hopper's paintings, "Nighthawks" (1942), is one of his paintings of a groups as it shows customers sitting at the counter of an all-night diner.
Split into simpler sentences: The best-known of Hopper's paintings, "Nighthawks" (1942), is one of his paintings of groups. It shows customers sitting at the counter of an all-night diner.