def max_possible_number(N, K, A):
    A = list(map(str, A)) 
    
    for _ in range(K):
        max_num = ''
        index = -1
        
       
        for i in range(N-1):
            new_num = A[i] + A[i+1]
            if new_num > max_num:
                max_num = new_num
                index = i
        
        if index == -1:
            break
        

        A[index] = max_num
        A.pop(index+1)
        N -= 1
    
    
    return max(A)

# input
T = int(input())
for _ in range(T):
    N, K = map(int, input().split())
    A = list(map(int, input().split()))
    print(max_possible_number(N, K, A))