1. (2020高三下·浙江月考) 数组a中存储了无序的数组元素，为了使a数组中的元素存储为左右交替上升，小赵依据选择排序思想设计了如下VB程序算法，为了实现上述功能，划线处应填入的代码为（  ）

L = 1: R = n

Do While L < R

imin_1 = L: imin_2 = R

    For i = L + 1 To R

        If a(i) < a(imin_1) Then

           imin_2 = imin_1

           imin_1 = i

        ElseIf a(i) < a(imin_2) Then

           imin_2 = i

        End If

    Next i

    If imin_1 <> L Then t = a(imin_1): a(imin_1) = a(L): a(L) = t

    ____________________

    If imin_2 <> R Then t = a(imin_2): a(imin_2) = a(R): a(R) = t

    L = L + 1: R = R - 1

Loop