The following program draws squares recursively. Fill in the missing code.

```
import javax.swing.*;
import java.awt.*;

public class Test extends JApplet {
public Test() {
add(new SquarePanel());
}

static class SquarePanel extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);

int width = (int)(Math.min(getWidth(), getHeight()) * 0.4);
int centerx = getWidth() / 2;
int centery = getHeight() / 2;

displaySquares(g, width, centerx, centery);
}

private static void displaySquares(Graphics g, int width,
int centerx, int centery) {
if (width >= 20) {
g.drawRect(centerx - width, centery - width, 2* width, 2 * width);
displaySquares(_________, width - 20, centerx, centery);
}
}
}
}
```
a. getGraphics()
b. newGraphics()
c. null
d. g

d. g