试述近5年来中国人民银行投放基础货币的主要渠道及其存在的问题。

[说明]
下面程序定义了一个类Point及其成员函数，然后从类Point派生出类Circle及其成员函数。
[Java程序]
class Mainjava
public static void main (String arg[])
Circle c=new Circle(2.5,3.7,4.3);
System.out.println(" X coordinate is "+c.getX()
+"\nRadius is: "+c.get Radius());
(1) ; //设置新的圆心(2，2)
Point pRef=c;
System.out.println("\n Circle printed as a point is : "
+"["+ (2) +"."+ (3) +"]"):


class Point
protected double x,y;
public Point (double a, double b) x = a; y = b;)
void setPoint (double a, double b) x = a; y = b;
final double getX () return x;
final double getY () return y;

class Circle (4)
protected double radius;
public Circle(double r, double a, double b)
(5) ;
radius=r ;
void setRadius (double r) radius=r;
final double getRadius () return radius;
final double area () return 3.14159*radius*radius;