问题：

[单选]

public class Mycircle {  
public double radius；  
public double diameter；  
public void setRadius（double radius）  
this.radius = radius；  
this.diameter= radius * 2；  
}  
public double getRadius（） { 
return radius；  
}  
Which statement is true？（）  

A .  The Mycircle class is fully encapsulated.
B .  The diameter of a given MyCircle is guaranteed to be twice its radius.
C .  Lines 6 and 7 should be in a synchronized block to ensure encapsulation.
D .  The radius of a MyCircle object can be set without affecting its diameter.