_______ his research, man can set foot on the moon now.

A．Because

B．Thanks to

C．So as to

D．In addition to

窗体上已有名称分别为Drive1、Dir1、File1的驱动器列表框、目录列表框和文件列表框，且有一个名称为Text1的文本框。以下程序的功能是：将指定位置中扩展名为".txt"的文件显示在File1中，如果双击File1中的某个文件，则在Text1中显示该文件的内容。请填空。
Private Sub Form_Load()
File1.Pattern= (13)
End Sub
Private Sub Drive1_Change()
Dir1.Path=Drive1.Drive
End Sub
Private Sub Dir1_Change()
File1.Path=Dir1.Path
End Sub
Private Sub File1_DblClick()
Dim S As String*1
If Right(File1.Path,1)="\"Then
f_name=File1.Path+Filel.FileName
Else
f_name=Filel.Path+"\"+Filel.FileName
End If
Open f_name (14) As#1
Text1.Text=" "
Do While (15)
s=Input(1，#1)
Text1, Text=Text1.Text+S
Loop
Close#1
End Sub