设有如下程序： Private Sub Command1_Click() Dim Sum As Double， x As Double sum=0 n = 0 For i= 1 To 5 x = n / i n = n + 1 sum=sum+x Next End Sub 该程序通过For循环计算一个表达式的值，这个表达式是

A．因果图
B．逻辑覆盖
C．循环覆盖
D．基本路径测试

A．Private Sub Text1_KeyPress(KeyAscii As Intege If Key Ascii＜65 Or KeyAscii＞90 Then MsgBox“请输入大写字母” KeyAscii=0 End If End Sub
B．Pfivate Sub Text1_KeyDown(KeyCode As Integer,Shift As Intege If KeyCode＜65 Or KeyCode＞90 Then MsgBox“请输入大写字母” KeyCode=0 End If End Sub
C．Private Sub Text1_MouseDown(Button As Integer，Shift As Integer，X As Single， Y As Singl If Asc(Text1.Tex＜65 Or Asc(Text1.Tex＞90 Then MsgBox“请输入大写字母” End If End Sub
D．Private Sub Text1_Change() If Asc(Text1.Tex＞64 And Asc(Text1.Tex＜91 Then MsgBox“请输入大写字母” End If End Sub