在算法执行过程中，关于“选择语句”，下列说法正确的是（   ）

A．顺序执行各语句

B．在预定的两个处理步骤中，按顺序各执行一次

C．根据不同的情况，在预定的两个处理步骤中，选择一个合适的处理步骤执行

D．对某个情况进行判断，当结果为真时重复执行步骤一，否则重复执行步骤二

（加试题）某VB程序使用了递归函数，代码如下：
Private Sub Command1_Click()
Text1.Text = f(3)
End Sub
Function f(x As Integer) As String
If x = 1 Then  f = 1  Else  f = f(x - 1) + 2
End Function
运行程序并点击按钮Command1后，文本框Text1中显示的内容是（ ）

A．1

B．3

C．5

D．7

Function f(x As Long, y As Long) As Long
Dim t As Long, r As Long
If x < y Then t =" x:" x =" y:" y = t
r =" x" Mod y
Do While r <> 0
x =" y:" y = r
r =" x" Mod y
Loop
f = y
End Function
-------------------------------------------------------------------------------------------------
Private Sub Command1_Click()
Dim a As Long, b As Long
x = Val(InputBox("x="))
y = Val(InputBox("y="))
a =" x:" b = y
s =" f(x," y)
MsgBox (Str(a * b / s))
End Sub
当x=20，y=6时，以上程序运行后，输出结果是（   ）

A．2

B．120

C．30

D．60

编写VB程序，实现如下功能：在文本框Text1 输入字母字符串，单击“加密”按钮Command1，字符进行逐个加密，加密过程是，先在“密码本”m中找到相应字符，再从Text3中得到其所对应位置的密钥,并在文本框Text2中显示密文（运行效果如下图所示）。本题暂时不考虑解密问题。实现上述功能的VB代码如下：

请在划线处填入合适代码。
Private SubCommand1_Click()
Dim s As String, m As String
Dim t As String
Dim k As String
Dim c As Integer
s = Text1.Text
n1 = Len(s)
s3 = Text3.Text
n3 = Len(s3)
If n3 < 26 Then
Label1.Caption = "请重新输入密钥！"
Text3.Text = ""
Exit Sub
End If
m = "abcdefghijklmnopqrstuvwxyz"
For i =" 1" To n1
k =" Mid(s," i, 1)
If ①Then    '将大写字母转换为小写
k =" Chr(Asc(k)" + 32)
End If
c = 1
Do While c <= Len(m)
If k =" Mid(m," c, 1) Then
Exit Do
End If
②
Loop
t =" t" +③
Next i
Text2.Text = t
End Sub

下列VB程序运行时，单击命令按钮Command1后，文本框Text1中显示的内容是（1）   ，文本框Text2中显示的内容是____（2）  。
Private Sub Command1_Click()
Dim i As Integer, c As Integer, n As Integer
c =" 0:" n = 10
For i =" 1" To n
If n Mod i =" 0" Then c =" c" + 1
Next i
Text1.Text = Str(n)
Text2.Text = Str(c)
End Sub