Function f(n As Integer) As Integer

  If n <= 1 Then

    f = 1

  Else

    f = n + f(n - 1)

  End If

End Function

Dim a(1 to 1000)as long, n as integer

n=Val(Text1.Text)

a(1)= 1:a(2)= 1

For i=3 to n

  a(i)= a(i-1)+a(i-2)

Next i

Label1.Caption=“斐波那契的第”&Str(n)&“是”&a(n)

该程序用到了下列哪一个算法（  ）

Function f(i As Integer)

    If i=1 Then

      f=2

    Else

      f=2 * 10 ^ (i-1)+f(i-1)

    End If

End Function

Private Sub Command1_Click()

    Dim n As Integer, s As Integer, i As Integer

    n=Val(Text1.Text)

    s=0

    For i=1 To n

      s=s+f(i)

    Next i

    Label1.Caption=Str(s)

End Sub

若在Text1中输入5，则Label1显示的内容为（  ）

F(1)=3

F(n)=F(n-1)*2

def f(n):

    if n == 5:

        return ___①___

    else:

        return _____②____

print(___③___)