B. collect(Collectors.toList()) Here's why: A. forEach(): This method is used for side effects on each element in the stream, not for collecting results into a List. It's not inherently thread-safe for modifying a collection concurrently. C. parallelStream(): This method simply creates a parallel stream from the original collection. It doesn't address thread safety during collection. D. stream(): This method creates a sequential stream. While it avoids the issue of parallel processing, it doesn't guarantee thread safety if the original collection is being modified concurrently. Collectors.toList(): When used with collect(), this collector provides thread-safe collection of elements from the stream into a new ArrayList instance. Java internally uses a thread-safe mechanism to handle concurrent additions to the list during parallel processing. Alternative for Thread Safety: CopyOnWriteArrayList: If you need to modify the original collection within the stream and maintain thread safety, consider using a CopyOnWriteArrayList instead of a regular List. This collection creates a copy of itself whenever a modification occurs, ensuring that the original list remains unmodified during the parallel processing. Example: Java import java.util.List; 39/97 import java.util.stream.Collectors; import java.util.stream.Stream; public class ThreadSafeCollection { public static void main(String[] args) { List numbers = List.of(1, 2, 3, 4, 5); // Option 1: Using collect(Collectors.toList()) List doubledNumbers = numbers.stream() .parallel() .map(number -> number * 2) .collect(Collectors.toList()); // Option 2: Using CopyOnWriteArrayList (if original list needs modification) List originalList = new CopyOnWriteArrayList<>(numbers); List tripledNumbers = originalList.stream() .parallel() .map(number -> number * 3) .collect(Collectors.toList()); System.out.println("Doubled numbers (thread-safe): " + doubledNumbers); System.out.println("Tripled numbers (thread-safe with CopyOnWriteArrayList): " + tripledNumbers); System.out.println("Original list remains unmodified: " + originalList); // If using CopyOnWriteArrayList } } In this example, both approaches ensure thread-safe collection: Option 1 uses collect(Collectors.toList()) for a new ArrayList creation within the parallel stream. Option 2 demonstrates using a CopyOnWriteArrayList as the original collection, ensuring thread safety even if the original list is being modified.