tc = int(input())
while tc:
    k = int(input())
    words = []
    for i in range(k):
        words.append(input())
    isans = False
    for i in range(k):
        for j in range(i + 1, k):
            temp1 = words[i] + words[j]
            temp2 = words[j] + words[i]
            if temp1[::-1] == temp1:
                print(temp1)
                isans = True
                break
            if temp2[::-1] == temp2:
                print(temp2)
                isans = True
                break
        if isans:
            break
    if not isans:
        print(0)
    tc -= 1
 

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