求的值，以下算法错误的是（  ）。

A．	B．
C．	D．

以下程序段运行时出现如图所示的错误提示:
 For i=1 To 100
If Rnd>0.5 Then
n=n+1
Else
m=m+1
Next i
分析该程序段,该代码中缺少了(  )

A．For

B．End If

C．Next

D．If

有如下VB程序段：
Private Sub Command1_Click()
Dim n As Integer, r As Integer, s As String
Dim t As Integer, k As Integer, v As Integer
n = 35: t = 0: k = 0
s = ""
Do While n > 0
r = n Mod 2
n = n \ 2
t = t + r
k = k + 1
s = Str(r) + s
Loop
s = Mid("0000000", 1, 7 - k) + s
v = t Mod 2
Text1.Text = s + Str(v)
End Sub
执行该程序段后，文本框Text1中显示的内容是

A．1 0 0 0 1 1 1

B．0 1 0 0 0 1 1 1

C．1 1 0 0 0 1 1

D．1 1 0 0 0 1 0 1

下列四段程序中，主要控制结构属于循环结构的是（   ）

A．A= 5 B= A A=" A" + B

B．IF X > K THEN PRINT "Big" END IF

C．S="0" DO WHILE I<=10 J =" I" * I S="S" + J I="I" + 1 LOOP

D．IF INT(X/2) = X/2 THEN

PRINT "偶数"
ELSE
PRINT "奇数"
END IF

编写VB程序，实现如下功能：在文本框Text1中输入一串字符，单击“统计”按钮Command1，统计每个英文字母（不区分大小写）出现的次数，找出出现次数最多的字母，在标签Label1中显示结果。运行效果如图所示。

实现上述功能的 VB 程序如下，请在划线处填入合适的代码。
Private Sub Command1_Click()
Dim i As Integer, n As Integer, max As Integer
Dim a(1 To 26) As Integer   '数组a存放26个大小写字母出现的次数Dim st As String, ch As String
st = Text1.Text
For i = 1 To Len(st)
    ①_____
If ch >= "A" And ch <= "Z" Then n = Asc(ch) - Asc("A") + 1  a(n) = a(n) + 1
ElseIf ch >= "a" And ch <= "z" Then n =    ②_____
a(n) = a(n) + 1
End If
Next i
max = a(1)
For i = 1 To 26
If      ③_____Then max = a(i)
End If Next i st = ""
For i = 1 To 26
If max = a(i) Then
st = st + " " + Chr(Asc("A") + i - 1) End If
Next i
Label1.Caption = "出现次数最多的字母是：" & st & " " & "出现次数为：" & Str(max)
End Sub
（2）在文本框 Text1 中输入字符串“ABCEEEEffee333333”，运行程序时，标签 Label1 中输出结果为：出现次数最多的字母是：_____出现次数为：_____。