Form_MouseDown (Button As Integer, Shift As Integer, X As Single, Y As Single)中参数分别代表什么意思？

窗体的MouseDown事件过程
Form_MouseDown (Button As Integer, Shift As Integer, X As Single, Y As Single)
有4个参数，关于这些参数，正确的描述是
A）通过Button参数判定当前按下的是哪一个鼠标键
B）Shift参数只能用来确定是否按下Shift键
C）Shift参数只能用来确定是否按下Alt和Ctrl键
D）参数x,y用来设置鼠标当前位置的坐标Form_MouseDown (Button As Integer, Shift As Integer, X As Single, Y As Single)中参数分别代表什么意思？