[单项选择] public class TestSeven extends Thread { private static int x; public synchronized void doThings() { int current = x; current++; x = current; } public void run() { doThings(); } } Which is true?() A. Compilation fails. B. An exception is thrown at runtime. C. Synchronizing the run() method would make the class thread-safe. D. The data in variable “x” are protected from concurrent access problems. E. Declaring the doThings() method as static would make the class thread-safe. F. Wrapping the statements within doThings() in a synchronized(new Object()) {} block would make the class thread-safe.