A. java List names = Arrays.asList("Alice", "Bob", "Charlie"); String allNames = names.stream().collect(Collectors.joining(",")); Here's why this option is correct: .collect(Collectors.joining(",")): This part uses the collect operation with the Collectors.joining collector. The joining collector is specifically designed for joining elements of a stream into a single String. You can specify a delimiter (", " in this case) to separate the elements in the joined String. The other options have limitations: B. StringBuilder sb = new StringBuilder(); ... sb.toString().substring(0, sb.length() - 1);: This approach uses a StringBuilder to manually append each element with a comma. While it works, it's less concise and efficient than using the Collectors.joining collector. The substring at the end is necessary to remove the trailing comma added after the last element C. String allNames = ""; names.stream().forEach(n -> allNames += n + ",");: This option also performs manual concatenation within a forEach loop. String concatenation within loops is generally less efficient than using a dedicated collector like Collectors.joining. Additionally, modifying a String object repeatedly within the loop can be less performant. Important Note: D. List names = Arrays.asList("Alice", null, "Charlie"); ...: The provided code snippet (regardless of the chosen option) would fail if the names list contains a null value. Streams cannot handle null values by default. You'll need to handle null values explicitly before using collect or any other stream operations. You can filter out null values or use a custom joining function that handles nulls appropriately