登录窗体如图所示，单击"登录"按钮，当用户名正确则弹出窗口显示"OK"信息。 A: PrivateSubcmdOK_Click()IftxtUser.Value="zhangs"ThenMsgBox"OK"EndifEndSub B: PrivateSubcmdOK_Click()IftxtUser.Value="zhangs"ThenMsgBox"OK"EndSub C: PrivateSubcmdOK_Click()IftxtUser.Value="zhangs"ThenMsgBox"OK"EndifEndSub D: PrivateSubcmdOK_Click()IftxtUser.Value="zhangs"MsgBox"OK"EndIfEndSub