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某教室在上午8点到12点的时间段可以安排活动。为了安排尽可能多场次的活动，按以下方法安排：先安排结束时间早的活动；若有多个活动的结束时间相同，则优先安排占用时间少的活动。要求编写一个VB程序，实现上述功能。在文本框Text1中输入一批数据（数据都用逗号分隔并以逗号结尾），奇数位置数据表示某活动的起始时间，偶数位置数据表示该活动的结束时间，单击“确定”按钮Command1后，在列表框List1中显示各活动的起始和结束时间，在列表框List2中显示选择安排的活动。运行界面如图所示。

（1）要清空Text1中的内容，可以把Text1对象的_________属性设置为空值。（单选，填字母：A．Caption / B．Text / C．Text．Clear）。
（2）实现上述功能的VB程序如下，请在划线处填入合适代码。
（3）程序加框处的代码有误，请改正。
Private Sub Command1_Click()
Const n = 100
Dim ss As String, t As String, i As Integer
Dim k As Integer, p As Integer, temp As Integer
Dim s(1 To n) As Integer, f(1 To n) As Integer
Dim num(1 To n) As Integer, flag(1 To n) As Boolean
ss = Text1．Text
starttime = 480: endtime = 720 '教室可以安排活动时间为8:00到12:00
k = 0: p = 0
For i = 1 To Len(ss)
ch = Mid(ss, i, 1)
If ch <> "," Then
t = t + ch
Else
____①
p = (k - 1) \ 2 + 1
If k Mod 2 = 1 Then s(p) = convert(t) Else f(p) = convert(t)
t = ""
End If
Next i
For i = 1 To p
num(i) = i
Next i
For i = 1 To p
List1．AddItem Str(num(i)) + "     " + ff(s(i)) + "     " + ff(f(i))
Next i
For i = 1 To p - 1
For j = p To i + 1 Step -1
If Then____
      temp = num(j): num(j) = num(j - 1): num(j - 1) = temp
      temp = s(j): s(j) = s(j - 1): s(j - 1) = temp
      temp = f(j): f(j) = f(j - 1): f(j - 1) = temp
End If
Next j
Next i
For i = 1 To p
If s(i) >= starttime And f(i) <= endtime Then
flag(i) = True
____②
End If
Next i
List2．AddItem "活动号 起始时间 结束时间"
For i = 1 To p
If____③ Then
List2．AddItem Str(num(i)) + "      " + ff(s(i)) + "     " + ff(f(i))
End If
Next i
End Sub
Function convert(s As String) As Integer
'把时间格式的s转换为整数，如"08:20"转化为500。代码略
End Function
Function ff(t As Integer) As String
'把整数t转换为时间格式，如500转化为"08:20"。代码略
End Function