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CAUTION: A ladder can be a very 1_______ tool. Any of these accidents could happen to you. (a) The ladder could slip on an oily 2_______ and you could fall off; (b) the top could fall backwards; (c) a door could open and push the 3_______ backwards or to the side; (d) a metal ladder could touch an 4_______ wire and give you an electric shock; (e) a ladder could fall off boxes or drums.