这道题我搞不懂,20.public class SychTest{ private int x; private int

这道题我搞不懂,20.public class SychTest{ private int x; private int y; public void setX(int i){ x=i;} public void setY(int i){y=i;} public Synchronized void setXY(int i){ setX(i); setY(i); } public Synchronized boolean check(){ return =y; } } Under which conditions will check() return true when called from a different class?A.check() can never return true.B.check() can return true when setXY is callled by multiple threads.C.check() can return true when multiple threads call setX and setY separately.D.check() can only return true if SychTest is changed allow x and y to be set separately.