gcj_2014_quals_c

for case in range(input()):
    print "Case #%d:" % (case+1)
    r,c,m = map(int, raw_input().split())
    flip = r>c
    if flip: c,r = r,c
    rem = r*c-m
    if r==1 or rem==1:
        res = ()
    elif r>1 and rem in {2,3,5,7} or (r==2 and rem%2):
        print "Impossible"
        continue
    elif rem <= 2*c+1:
        res = (rem//2-rem%2,)*2
    else:
        res = (c,)*(rem//c-1) + (c-(rem%c==1),)
    res = (res + (rem-sum(res),) + (0,)*r)[:r]
    board = ["."*res[i]+"*"*(c-res[i]) for i in range(r)]
    board[0] = "c" + board[0][1:]
    if flip: board = zip(*board)
    for row in board: print "".join(row)