1. 下列VB程序段功能为：在文本框Text1中显示整型数组元素a(1)到a(9)中的最小值和最大值。

amin = a(1): amax = a(1)

i = 2: j = 9

Do While i <= j

    If a(i) > a(j) Then

       

       

    Else

       

       

    End If

    i = i + 1: j = j - 1

Loop

Text1.Text = Str(amin) + "," + Str(amax)

上述程序段中方框处可选语句为：

①If a(j) > amax Then amax = a(j)

②If a(j) < amin Then amin = a(j)

③If a(i) < amin Then amin = a(i)

④If a(i) > amax Then amax = a(i)

则方框处语句依次可为（    ）