MAC how to copy paste under xterm

Firstly, introduce how to give a screenshot in the mac：

在Mac上截图其实很简单，但很多人只知道Command-Shift-3和Command-Shift-4，却不知道Mac的截图快捷键其实还有很多增强，具体如下： 
1)Command-Shift-3: 将整个屏幕拍下并保存到桌面。 
2)Command-Shift-Control-3:将整个屏幕拍下并保存到剪贴板(Clipboard)，你可以Command+V直接粘贴到如Photoshop等软件中编辑。 
3)Command-Shift-4:将屏幕的一部分拍下并保存到桌面。按下这个组合键后，光标会变为一个十字，你可以拖拉来选取拍摄区域。 
4)Command-Shift-Control-4:将屏幕的一部分拍下并保存到剪贴板。 
5)Command-Shift-4再按空格键:这时光标会变为一个照相机图标，点击可拍下当前窗口或菜单或Dock以及图标等，只要将照相机图标移动到不同区域（有效区域会显示为浅蓝色）点击。 
6)Command-Shift-Control-4再按空格键:将选取的窗口或其他区域的快照保存到剪贴板。
from: http://hi.baidu.com/ricestudio/item/5a42d614cdbb254fe75e065b

Then, let s talk about how to copy and paste under xterm which make me puzzle for one month:

copy    command + C as usual
pase    
(1) for touch pad:
   option+ click
(2) for mouse:
   option+ click
It is easy!  However, you should enable the three button mouse. It can be found in the preference of x11 or Xquartz. See the first first tick bellow: