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学校创客社团开展机器人比赛活动,其中设置了机器人循迹项目。比赛规则如下:给出10*10规模的矩阵地图，随机设定4个循迹点，小车以蛇形路线找到循迹点后，计算最长的两点直线距离。矩阵图中以0表示非循迹点，1表示循迹点，循迹过程如图a所示：编写一个VB程序实现如下功能：单击“开始循迹”按钮Command1，呈现10*10矩阵地图，并随机生成4个循迹点，分别用数字1表示，数字0表示非循迹点；计算4点中相距最远的两点的直线距离，显示在标签Label1中。程序运行界面如图b所示。

图a                                                                                                                                                             图b
（1）若随机生成的4个循迹点如图a所示，则该4点中相距最远的两点直线距离为_________。
（2）实现上述功能的VB程序如下，请在划线处填入合适的代码。
Const n = 10, m=4
Dim b(1 To 8) As Integer
Private Sub Command1_Click()
Dim f(1 To n * n) As Integer
Dim i As Integer, j As Integer, w As Integer, k As Integer
Dim length As Single, maxlen As Single, s As String
‘生成矩阵地图和随机生成4个循迹点,0表示非循迹点,1表示循迹点,存于数组f中For i = 1 To n^2 ‘显示矩阵地图和4个循迹点

s = s + Str(f(i))

If i Mod n = 0 Then

List1.AddItem s

s=""

End If

Next i
w = 1
For i = 1 To n

For j = 1 To n

k = (n + 1) * ((i-l) Mod 2)+(-1)^(i-1)*j

If_____① Then‘记录循迹点所在位置

b(2 * w - 1) = i: b(2 * w) = k

w = w + 1

End If

Next j

Next i
i=1 : maxlen = 0
Do While i<= m - 1

For j=i+1 To m

   ______②     

If length > maxlen Then maxlen = length

Next j

i = i + 1

Loop
Label1.Caption = Str(maxlen)
End Sub
Function reck(x As Integer, y As Integer) As Single
Dim c As Integer, d As Integer
Dim h As Single
c =______③      
d = Abs(b(2 * x)-b(2 * y))
h= Sqr(c^2+d^ 2)
reck = h
End Function