问题 选择题

科学家利用转基因技术,使大肠杆菌产生大量的胰岛素,用来拯救糖尿病患者.这是利用了大肠杆菌的哪一特点(  )

A.个体小,容易控制

B.分布广,成本较低

C.短期内能快速繁殖

D.不易被其它细菌感染

答案

把一种生物的某个基因,用生物技术的方法转入到另一种生物的基因组中,培育出的转基因生物,就有可能表现出转入基因所控制的性状.科学家把控制合成胰岛素的基因转入大肠杆菌内,在条件适宜时,大肠杆菌繁殖快,可在短时间内生产出大量的治疗糖尿病的药物--胰岛素.

故选:C

选择题
问答题

本题中,鼠标在窗口中单击一下,就在单击的位置生成一个小矩形,如果在小矩形上双击鼠标左键,则删除小矩形。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class MousePanel extends JPanel extends MouseMotionListener
public MousePanel()
addMouseListener(new MouseAdapter()
public void mousePressed(MouseEvent evt)
int x=evt.getX();
int y=evt.getY();
current=find(x,y);
if(current<0)
add(x,y);

public void mouseClicked(MouseEvent evt)
int x=evt.getX();
int y=evt.getY();
if(evt.getClickCount()>=2)
remove(current);


);
addMouseMorionListener(this);

public void paintComponent(Graphics g)
(super.paintComponent();
for(int i=0;i<nsquares;i++)
draw(g,i);

public int find(int x,int y)
for(int i=0;i<nsquares;i++)
if(squares[i].x-SQUARELENGTH/2<=x&&
x<=squares[i].x+SQUARELENGTH/2
&&squares[i].y-SQUARELENGTH/2<=y
&&y<=squares[i].y+SQUARELENGTH/2)
return i;
return-1;

public void draw(Graphics g,int i)
g.drawRect(squares[i].x-SQUARELENGTH/2,
squares[i].y-SQUARELENGTH/2,
SQUARELENGTH,
SQUARELENGTH);

public void add(int x,int y)
if(nsquares<MAXNSQUARES)
squares[nsquares]=new Point(x,y);
current=nsquares;
nsquares++;
repaint();


public void remove(int n)
if(n<0 || n>=nsquares)return;
nsquares--;
squares[n]=squares[nsquares];
if(current==n)current=-1;
repaint();

public void mouseMoved(MouseEvent evt)

public void mouseDragged(MouseEvent evt)

private static final int SQUARELENGTH=10;
private static final int MAXNSQUARES=100;
private Point[] squares=new Point[MAXNSQUARES];
private int nsquares=0;
private int current=-1;

class MouseFrame extends JFrame
public MouseFrame()
setTitle("java3");
setSize(300,200);
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System.exit(0);

);
Container contentPane=getContentPane();
contentPane.add(MousePanel());


public class java3
public static void main(String[]args)
JFrame frame=new MouseFrame();
frame.show();