单选题 下面的程序是利用公式：π=4-4/3+4/5-4/7+4/9-4/11+…计算π的近似值
Pvivate Sub Command1_Click()
Dim PI As Double, x As Double, k As Long, sign As Integer
sign=1
k=1
PI=0
Do
x=sign*4/(2*k-1)
PI=PI+x
k=k+1
sign=______
Loop Until Abs(x)＜0.000001
Print PI
End Sub
在空处应填写的是______。