1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for _ in range(int(input())):
    n=int(input())
    lst=[int(x) for x in input().split()]
    m = max(lst)
    k = lst.index(m)
    if k:
        print(k + 1)
    else:
        for i in range(1, n):
            if lst[i] != m:
                print(k + 1)
                break
            k = i
        else:
            print(-1)