灰度等级为256，分辨率为1024*1024的显示器，至少需要的帧缓存容量为（）
A.512KB
B.1MB
C.2MB
D.3MB
参考答案：B
His grandfather ________ for seven years.
A．died
B．had died
C．has died
D．has been dead
试述购买行为的特征？
