Which code segment should you insert at line 09?

You are developing an application that will use multiple asynchronous tasks to optimize performance.
You create three tasks by using the following code segment. (Line numbers are included for reference only.)

You need to ensure that the ProcessTasks() method waits until all three tasks complete before continuing.
Which code segment should you insert at line 09?
A. Task.WaitFor(3);
B. tasks.Yield();
C. tasks.WaitForCompletion();
D. Task.WaitAll(tasks);