def min_new(a, m):
    while m in a:
        m+=1
    return m

def max_new(a: set[int], m):
    while m in a:
        m-=1

    return m

def get_minimal(a, n):
    used = set(a)
    if len(used) != len(a):
        return [-1]

    arr = []
    for i in range(n//2):
        m = max_new(used, a[i])
        used.add(m)
        if m <= 0:
            return [-1]

        arr.append(m)

    for i in range(n//2):
        for j in range(i, n//2):
            if arr[j] < arr[i] and arr[i] < a[j]:
                tmp = arr[j]
                arr[j] = arr[i]
                arr[i] = tmp

    return arr

# Réécrire en c++
def main():
    ct = int(input())

    for i in range(ct):
        n = int(input())
        a = [int(b) for b in input().split()]

        arr = get_minimal(a, n)
        if arr == [-1]:
            print(-1)
        else:
            print(" ".join([str(arr[i])+" "+str(a[i]) for i in range(len(arr))]))

main()