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

t = int(input().strip())
while(t):
    n = int(input().strip())
    a = list(map(int, input().strip().split()))
    seta = set(a)
    if len(seta) == 1:
        print(-1)
    else:
        mval = 0 
        index = -1
        for i in range(n):
            if a[i] > mval :
                mval = a[i]
                index = i
        print(index+1)
    
    
    t -= 1